Upgrade to v0.44

Breaking change

Because of a TLS lib issue, we temporarily disable the services-ftp feature.

Operator and BlockingOperator won't accept layers anymore. Instead, we provide a layer API:

op = opendal.Operator("memory").layer(opendal.layers.RetryLayer())

We removed not used layers ConcurrentLimitLayer and ImmutableIndexLayer along with this change.

OpenDAL removes Reader and AsyncReader classes, instead, we provide file-like object File and AsyncFile.

Open a file for reading in blocking way:

with op.open(filename, "rb") as r:
    content = r.read()

Open a file for reading in async way:

async with await op.open(filename, "rb") as r:
    content = await r.read()

We remove the old error classes and provide a couple of Exception based class for the error handling.