add --strict-bytes to --strict

[wyattscarpenter]

This is a check that ensures static correctness, so it is useful to have in --strict. Unlike making this the default behavior eventually in 2.0, which we are also planning to do, it can be added to --strict immediately due to --strict having looser backwards-compatibility requirements (or so I interpret --strict's documentation). This PR also includes tests, for --strict and also for no flags.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

mongo-python-driver (https://github.com/mongodb/mongo-python-driver)
+ pymongo/network_layer.py:351: error: Argument 1 to "recv_into" of "NetworkingInterface" has incompatible type "memoryview[int]"; expected "bytes"  [arg-type]
+ pymongo/network_layer.py:767: error: Argument 1 to "decompress" has incompatible type "memoryview[int]"; expected "bytes"  [arg-type]
+ pymongo/network_layer.py:769: error: Incompatible types in assignment (expression has type "memoryview[int]", variable has type "bytes")  [assignment]
+ pymongo/message.py:738: error: Argument 1 to "_inflate_bson" has incompatible type "memoryview[int]"; expected "bytes"  [arg-type]
+ pymongo/asynchronous/encryption.py:212: error: Incompatible types in assignment (expression has type "memoryview[int]", variable has type "bytes")  [assignment]

boostedblob (https://github.com/hauntsaninja/boostedblob)
+ boostedblob/write.py:67: error: Argument "data" to "Request" has incompatible type "Union[bytes, bytearray, memoryview[int]]"; expected "Union[Dict[str, Any], bytes, None]"  [arg-type]
+ boostedblob/write.py:88: error: Argument "data" to "Request" has incompatible type "Union[bytes, bytearray, memoryview[int]]"; expected "Union[Dict[str, Any], bytes, None]"  [arg-type]
+ boostedblob/write.py:411: error: Argument "data" to "Request" has incompatible type "Union[bytes, bytearray, memoryview[int]]"; expected "Union[Dict[str, Any], bytes, None]"  [arg-type]

bokeh (https://github.com/bokeh/bokeh)
+ src/bokeh/core/serialization.py: note: In member "_decode_bytes" of class "Deserializer":
+ src/bokeh/core/serialization.py:618:16: error: Incompatible return value type (got "bytes | memoryview[int]", expected "bytes")  [return-value]

websockets (https://github.com/aaugustin/websockets)
+ src/websockets/streams.py:52: error: Incompatible return value type (got "bytearray", expected "bytes")  [return-value]
+ src/websockets/streams.py:75: error: Incompatible return value type (got "bytearray", expected "bytes")  [return-value]
+ src/websockets/streams.py:97: error: Incompatible return value type (got "bytearray", expected "bytes")  [return-value]
+ src/websockets/frames.py:174: error: Argument 1 to "parse" of "Close" has incompatible type "bytes | bytearray | memoryview[int]"; expected "bytes"  [arg-type]
+ src/websockets/frames.py:328: error: Argument 1 to "apply_mask" has incompatible type "bytes | bytearray | memoryview[int]"; expected "bytes"  [arg-type]
+ src/websockets/frames.py:330: error: Incompatible types in assignment (expression has type "bytes | bytearray | memoryview[int]", variable has type "bytes")  [assignment]
+ src/websockets/protocol.py:706: error: Argument 1 to "parse" of "Close" has incompatible type "bytes | bytearray | memoryview[int]"; expected "bytes"  [arg-type]
+ src/websockets/extensions/permessage_deflate.py:137: error: Incompatible types in assignment (expression has type "bytes | bytearray | memoryview[int]", variable has type "bytes")  [assignment]
+ src/websockets/extensions/permessage_deflate.py:194: error: Incompatible types in assignment (expression has type "memoryview[int]", variable has type "bytes")  [assignment]
+ src/websockets/asyncio/messages.py:246: error: Incompatible types in "yield" (actual type "bytes | bytearray | memoryview[int]", expected type "str | bytes")  [misc]
+ src/websockets/asyncio/messages.py:260: error: Incompatible types in "yield" (actual type "bytes | bytearray | memoryview[int]", expected type "str | bytes")  [misc]
+ src/websockets/asyncio/connection.py:487: error: Argument 1 to "send_text" of "Protocol" has incompatible type "bytes | memoryview[Any]"; expected "bytes"  [arg-type]
+ src/websockets/asyncio/connection.py:489: error: Argument 1 to "send_binary" of "Protocol" has incompatible type "bytes | memoryview[Any]"; expected "bytes"  [arg-type]
+ src/websockets/sync/messages.py:258: error: Incompatible types in "yield" (actual type "bytes | bytearray | memoryview[int]", expected type "str | bytes")  [misc]
+ src/websockets/sync/messages.py:269: error: Incompatible types in "yield" (actual type "bytes | bytearray | memoryview[int]", expected type "str | bytes")  [misc]
+ src/websockets/legacy/framing.py:117: error: Argument 3 to "Frame" has incompatible type "bytes | bytearray | memoryview[int]"; expected "bytes"  [arg-type]
+ src/websockets/sync/connection.py:486: error: Argument 1 to "send_text" of "Protocol" has incompatible type "bytes | memoryview[Any]"; expected "bytes"  [arg-type]
+ src/websockets/sync/connection.py:488: error: Argument 1 to "send_binary" of "Protocol" has incompatible type "bytes | memoryview[Any]"; expected "bytes"  [arg-type]
+ src/websockets/legacy/protocol.py:631: error: Argument 1 to "prepare_data" has incompatible type "str | bytes | memoryview[Any]"; expected "str | bytes"  [arg-type]
+ src/websockets/sync/client.py:645: error: Argument 1 to "send" of "SSLSSLSocket" has incompatible type "memoryview[int]"; expected "bytes"  [arg-type]

python-chess (https://github.com/niklasf/python-chess)
+ chess/gaviota.py:1738: error: Incompatible types in assignment (expression has type "bytearray", variable has type "bytes")  [assignment]

werkzeug (https://github.com/pallets/werkzeug)
+ src/werkzeug/sansio/multipart.py:174: error: Argument 1 to "_parse_headers" of "MultipartDecoder" has incompatible type "bytearray"; expected "bytes"  [arg-type]
+ src/werkzeug/sansio/multipart.py:213: error: Argument 1 to "_parse_data" of "MultipartDecoder" has incompatible type "bytearray"; expected "bytes"  [arg-type]
+ src/werkzeug/sansio/multipart.py:220: error: Argument 1 to "_parse_data" of "MultipartDecoder" has incompatible type "bytearray"; expected "bytes"  [arg-type]

[sterliakov]

I think this is a good suggestion. Probably needs a visible changelog entry (not only in "other changes" list), but this flag really belongs to --strict group IMO as it can actually flag unsound code and isn't linter-ish. Given the desire to enable it in 2.0, I think adding this flag to --strict will increase its exposure before it's too late.