br: fix fast compact bugs

[RidRisR]

What problem does this PR solve?

1. If we use checkpoint span as the only indicator on compact or not, when the log backup checkpoint get stuck, the progress [last compact, checkpoint] would not be compact due to (checkpoint - last compact)<compact_span

2. If the last_backup_ts exceeds the checkpoint, we should also set it as next_compact_ts for alignment.

What is changed and how does it work?

1. Now, the schedule will try to do a routine compact every compact_interval if it is not behind last backup.
2. Modified the calEndTs func so that we could record the next_compact_ts even if last_backup_ts exceeds fastCompactLimit
3. Two new unit tests are added.

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

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[RidRisR]

/retest

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 50 lines in your changes missing coverage. Please review.

Project coverage is 45.63%. Comparing base (a16b2e8) to head (86d35d5).
Report is 27 commits behind head on master.

❗ Current head 86d35d5 differs from pull request most recent head 384b311

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HEAD has 1 upload less than BASE

Flag	BASE (a16b2e8)	HEAD (86d35d5)
unittest	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #6103       +/-   ##
===========================================
- Coverage   57.19%   45.63%   -11.57%     
===========================================
  Files         259      223       -36     
  Lines       33233    32061     -1172     
===========================================
- Hits        19008    14631     -4377     
- Misses      12291    15588     +3297     
+ Partials     1934     1842       -92     

Flag	Coverage Δ
e2e	45.63% <0.00%> (?)
unittest	?

[WangLe1321]

The comments of LastCompactProgress and LastCompactExecutionTs are same, and what's the difference between them?