parsers: fix typing in socket.py

[mkmkme]

Pull Request check-list

Make mypy slightly happier by fixing some typing in socket.py

• 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)?

Description of change

[codecov-commenter]

Codecov Report

❌ Patch coverage is 78.57143% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.80%. Comparing base (f991654) to head (79c0e19).

Files with missing lines	Patch %	Lines
valkey/_parsers/socket.py	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #224      +/-   ##
==========================================
- Coverage   76.30%   73.80%   -2.51%     
==========================================
  Files         130      130              
  Lines       33954    33958       +4     
==========================================
- Hits        25909    25062     -847     
- Misses       8045     8896     +851     

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[mkmkme]

Okay apparently None is a valid value here that we'd like to pass, this is causing tests to fail.
In order to make mypy happier, I'll need TypeGuard that is introduced in 3.10, so I'll wait until #220 is merged.