*: reduce NewRuntimeStatsColl() object allocation

[tiancaiamao]

What problem does this PR solve?

Take part of the code from #26007
ResetContextStmt is not touched

What is changed and how it works?

What's Changed:

How it Works:

Change NewRuntimeStatsColl() to NewRuntimeStatsColl(*RuntimeStatsColl) so when the argument is not nil, the object is reused.

Check List

Tests

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

Documentation

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

Release note

• No release note

[tiancaiamao]

For #25573

[ti-chi-bot]

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[crazycs520]

LGTM

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[tiancaiamao]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 9d86160