executor: Optimize slow log parsing's splitByColon function (#54630)

[ti-chi-bot]

This is an automated cherry-pick of #54630

What problem does this PR solve?

Issue Number: close #54538

Problem Summary:

What changed and how does it work?

Replace regexp matching with simple string comparison operations. Besides, previously, ":=" inside "{}" are not handled correctly, fix it in this PR also.
In local mannual test, performance will improve about 10x, from 24s to 2.2s for the following sql:
SELECT Digest, Query, Conn_ID, (UNIX_TIMESTAMP(Time) + 0E0) AS timestamp, Query_time, Mem_max, Process_keys FROM `INFORMATION_SCHEMA`.`CLUSTER_SLOW_QUERY` WHERE Time BETWEEN FROM_UNIXTIME(1720471890) AND FROM_UNIXTIME(1720515091) ORDER BY Query_time DESC LIMIT 100;

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[windtalker]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 89.04110% with 8 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-6.5@1203ea2). Learn more about missing BASE report.

Additional details and impacted files

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: guo-shaoge, windtalker

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-03 06:56:10.346467023 +0000 UTC m=+341094.864520125: ☑️ agreed by windtalker.
• 2024-09-03 08:08:29.565823989 +0000 UTC m=+345434.083876913: ☑️ agreed by guo-shaoge.

[yibin87]

/test unit-test

[tiprow]

@yibin87: No presubmit jobs available for pingcap/tidb@release-6.5

In response to this:

/test unit-test

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