Add BITFIELD_RO

[bodevone]

Pull Request check-list

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

• [ ] Does $ tox pass with this change (including linting)?
• [ ] 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

Add BITFIELD_RO

[codecov-commenter]

Codecov Report

Merging #2340 (3d5884d) into master (771109e) will decrease coverage by 13.62%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master    #2340       +/-   ##
===========================================
- Coverage   92.19%   78.56%   -13.63%     
===========================================
  Files         111      111               
  Lines       28751    28776       +25     
===========================================
- Hits        26507    22609     -3898     
- Misses       2244     6167     +3923     

Impacted Files	Coverage Δ
redis/commands/core.py	82.00% <100.00%> (-0.11%)	:arrow_down:
tests/test_asyncio/test_commands.py	98.39% <100.00%> (+<0.01%)	:arrow_up:
tests/test_commands.py	89.71% <100.00%> (-0.10%)	:arrow_down:
tests/test_cluster.py	18.58% <0.00%> (-78.50%)	:arrow_down:
tests/test_asyncio/test_cluster.py	18.88% <0.00%> (-78.40%)	:arrow_down:
redis/asyncio/cluster.py	16.52% <0.00%> (-73.77%)	:arrow_down:
redis/cluster.py	18.81% <0.00%> (-71.04%)	:arrow_down:
redis/asyncio/parser.py	17.30% <0.00%> (-63.47%)	:arrow_down:
redis/commands/cluster.py	37.57% <0.00%> (-56.07%)	:arrow_down:
redis/crc.py	45.45% <0.00%> (-54.55%)	:arrow_down:
... and 27 more

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