Use CPU based limit and Blocking Connection Pool in redis-py by default

[dvora-h]

Pull Request check-list

Please make sure to review and check all of these items:

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Please provide a description of the change here.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 91.81%. Comparing base (2f88840) to head (20c0721).
Report is 20 commits behind head on master.

Files	Patch %	Lines
redis/connection.py	38.23%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3200      +/-   ##
==========================================
- Coverage   91.84%   91.81%   -0.04%     
==========================================
  Files         128      128              
  Lines       33232    33354     +122     
==========================================
+ Hits        30523    30625     +102     
- Misses       2709     2729      +20     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[gerzse]

I see three different things in this PR:

• Switch to BlockingConnection
• Limit the number of connections to 2 * CPU_COUNT, by default
• Some new methods added related to caching

The first two changes seem pretty relevant to me, so that they deserve explanations in the commit messages: why were they done, what triggered them, etc.

[gerzse]

Remove the fixture from here, if initialized inside the test?