skip ssl import if not available

[dicej]

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Description of change

utils.py has support for detecting whether the ssl module is available, and we can use this to omit SSL-specific funcionality while still providing other features (e.g. unencrypted connections).

Prior to this patch, the connection.py modules both triggered an ImportError due to unconditional imports of the ssl module. Now, we check utils.SSL_AVAILABLE prior to attempting the import and only raise an error later if (and only if) the application requests an encrypted connection. This helps support platforms such as wasm32-wasi where the ssl module is not built by default.

Ideally, this would be tested in CI using a Python built without ssl support. I'm not sure how feasible that is, though; I'm open to guidance on that aspect.

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (2f88840) 91.84% compared to head (b94b105) 91.83%.
Report is 8 commits behind head on master.

Files	Patch %	Lines
redis/asyncio/connection.py	63.63%	4 Missing ⚠️
redis/connection.py	66.66%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3078      +/-   ##
==========================================
- Coverage   91.84%   91.83%   -0.01%     
==========================================
  Files         128      128              
  Lines       33232    33283      +51     
==========================================
+ Hits        30523    30567      +44     
- Misses       2709     2716       +7     

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[petyaslavova]

Hi @dicej, can you please update your code to follow the pattern set in https://github.com/redis/redis-py/blob/master/redis/client.py for ssl import and type hints and fix the conflicts?

[petyaslavova]

Requested changes are posted in previous comment.

[dicej]

Hi @dicej, can you please update your code to follow the pattern set in https://github.com/redis/redis-py/blob/master/redis/client.py for ssl import and type hints and fix the conflicts?

Done, and tested on wasm32-wasi (which does not have an ssl module).

[petyaslavova]

@dicej please fix the linter errors and apply requested changes