Fix cluster pipeline retries for connection timeouts

[mkmkme]

Reuse the shared cluster reinitialize error set so pipeline connection checkout timeouts refresh topology and retry like single commands. Add sync regression coverage for get_connection() timeouts and an asyncio guard test for existing retry behavior.

Fixes #261

Pull Request check-list

• 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

[Copilot]

Pull request overview

This PR aligns cluster pipeline retry behavior with single-command execution so that connection checkout timeouts trigger topology refresh + retry, and adds regression coverage for both sync and asyncio clients.

Changes:

• Introduces a shared REINITIALIZE_ERRORS tuple on AbstractValkeyCluster and reuses it in ClusterPipeline.
• Updates ClusterPipeline.send_cluster_commands() / _send_cluster_commands() to reinitialize and retry on connection checkout TimeoutError (and other reinit-worthy errors).
• Adds sync regression tests for get_connection() timeout retry/raise behavior and an asyncio guard test for timeout retry behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
valkey/cluster.py	Unifies retryable reinit errors and extends pipeline retry/reinitialize behavior to include connection checkout timeouts.
tests/test_cluster.py	Adds sync regression tests covering timeout retry and exhausted-retry behavior for pipeline connection acquisition.
tests/test_asyncio/test_cluster.py	Adds asyncio test ensuring pipeline retries on TimeoutError during execution.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.45%. Comparing base (98d3b5c) to head (134016b).
⚠️ Report is 89 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #284      +/-   ##
==========================================
+ Coverage   76.40%   76.45%   +0.05%     
==========================================
  Files         129      129              
  Lines       34065    34125      +60     
==========================================
+ Hits        26027    26090      +63     
+ Misses       8038     8035       -3     

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[mkmkme]

@copilot review

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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