improve the PublicTopicReaderPartitionExpiredError description

[AlejandroMokhovani]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Other information

Extended description of PublicTopicReaderPartitionExpiredError with developer guidance on next steps.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.33%. Comparing base (5ff1186) to head (2ef20dd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #869      +/-   ##
==========================================
- Coverage   82.97%   82.33%   -0.64%     
==========================================
  Files          99       99              
  Lines       12749    12749              
  Branches     1242     1242              
==========================================
- Hits        10578    10497      -81     
- Misses       1775     1797      +22     
- Partials      396      455      +59     

Flag	Coverage Δ
integration	80.21% <ø> (+0.04%)	⬆️
unit	48.37% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ydb/_topic_reader/topic_reader_asyncio.py	86.89% <ø> (ø)

... and 4 files with indirect coverage changes

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[weres-sa]

LGTM