mounter(ticdc): optimize mounter cpu usage by reduce memory allocation on map and slice

[3AceShowHand]

What problem does this PR solve?

Issue Number: close #11210

What is changed and how it works?

• use sync.Pool to reduce the map allocation for the datum
• remove columnInfo slice from the datums2Column method, to reduce memory allocation.

Check List

Tests

• Unit test
• Integration test

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

`None`

[codecov]

Codecov Report

Attention: Patch coverage is 92.15686% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 57.6113%. Comparing base (7fbae79) to head (57b01d9).
Report is 1 commits behind head on master.

❗ Current head 57b01d9 differs from pull request most recent head f59703a

Please upload reports for the commit f59703a to get more accurate results.

Additional details and impacted files

Components	Coverage Δ
cdc	61.4317% <92.1568%> (-0.0518%)	⬇️
dm	51.1638% <ø> (-0.0424%)	⬇️
engine	63.4020% <ø> (+0.0494%)	⬆️

Flag	Coverage Δ
unit	57.6113% <92.1568%> (-0.0363%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             master     #11081        +/-   ##
================================================
- Coverage   57.6475%   57.6113%   -0.0363%     
================================================
  Files           850        850                
  Lines        126040     126055        +15     
================================================
- Hits          72659      72622        -37     
- Misses        47985      48026        +41     
- Partials       5396       5407        +11     

[CharlesCheung96]

Please add the test result.

[3AceShowHand]

Please add the test result.

The metrics is lost, since I use continous profiling which delete metrics data each 3 hours.

On the master branch, we can see obvious makemap called inside the decodedRowV2 method, and makeslice around 2.0% CPU usage inside the datum2Columns method.

In this PR, the makemap cannot be seen, and makeslice reduced to around 1.1%.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CharlesCheung96

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• OWNERS [CharlesCheung96]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-31 08:04:22.765480925 +0000 UTC m=+3022816.522616496: ☑️ agreed by CharlesCheung96.