tso: speed up tso update for release-8.5-20251204-v8.5.4

[bufferflies]

What problem does this PR solve?

Issue Number: Close #10138
cp link：https://github.com/tikv/pd/pull/10137/changes

What is changed and how does it work?

1. Advance the physical timestamp by the GetTs request, not only by the ticker.
2. Only the ticker can save the timestamp into the storage when it reaches the save time to avoid frequent updating. 

Check List

Tests

• Unit test
• manual test

tiup playground nightly --pd 1 --kv 1 --tiflash 0 --db 0 --pd.host 10.138.0.52 --pd.config pd.toml --pd.binpath ./pd/bin/pd-server
./bin/pd-tso-bench -pd 10.138.0.52:2379 -client 500 -duration 10m -c 10

Master(tso-update-physical-interval = "2s"):

This PR(tso-update-physical-interval = "2s")

Code changes

Side effects

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Release note

None.

Summary by CodeRabbit

• New Features

  • Added an observability metric to surface when saving timestamps is disallowed.

• Bug Fixes

  • Retry logging for timestamp updates now includes an overflow indicator and returns the final attempt outcome.
  • Timestamp persistence is gated to avoid unintended physical updates.
  • Improved synchronization to reduce unnecessary physical timestamp changes.

• Tests

  • Added tests for timestamp generation, guarded-save behavior, logical overflow, and concurrent access.

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[codecov]

Codecov Report

❌ Patch coverage is 82.92683% with 7 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5-20251204-v8.5.4@34c6617). Learn more about missing BASE report.

Additional details and impacted files

@@                      Coverage Diff                       @@
##             release-8.5-20251204-v8.5.4   #10693   +/-   ##
==============================================================
  Coverage                               ?   78.18%           
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  Files                                  ?      469           
  Lines                                  ?    64493           
  Branches                               ?        0           
==============================================================
  Hits                                   ?    50426           
  Misses                                 ?    10421           
  Partials                               ?     3646           

Flag	Coverage Δ
unittests	78.18% <82.92%> (?)

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[bufferflies]

ref #10702