keyspace: Asynchronously pre-allocate keyspaces

[pingyu]

What problem does this PR solve?

Issue Number: Close #9022

What is changed and how does it work?

keyspace: Asynchronously pre-allocate keyspaces to improve startup performance (mainly for test).

Please note that this PR introduce some changes, including:

• The rule of wait split region,
• The time when keyspaces are created,
• And the keyspace ids are not determined.

So this PR modify some unit test cases to meet the changes.

Check List

Tests

• Unit test
• Integration test

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

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

Release note

keyspace: Asynchronously pre-allocate keyspaces to improve startup performance (mainly for test).

[codecov]

Codecov Report

Attention: Patch coverage is 47.82609% with 12 lines in your changes missing coverage. Please review.

Project coverage is 75.74%. Comparing base (9092ccc) to head (afcd7a9).
Report is 1 commits behind head on master.

❌ Your patch status has failed because the patch coverage (47.82%) is below the target coverage (74.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9019      +/-   ##
==========================================
+ Coverage   75.72%   75.74%   +0.01%     
==========================================
  Files         477      477              
  Lines       73437    73438       +1     
==========================================
+ Hits        55612    55623      +11     
+ Misses      14342    14334       -8     
+ Partials     3483     3481       -2     

Flag	Coverage Δ
unittests	75.74% <47.82%> (+0.01%)	⬆️

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[pingyu]

/retest

[ti-chi-bot]

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AmoebaProtozoa, nolouch, rleungx

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• OWNERS [nolouch,rleungx]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-04-08 09:04:50.432484698 +0000 UTC m=+2160784.116720794: ☑️ agreed by nolouch.
• 2025-04-08 09:27:38.462945804 +0000 UTC m=+2162152.147181899: ☑️ agreed by rleungx.