[improve][fn] Use PulsarByteBufAllocator.DEFAULT instead of ByteBufAllocator.DEFAULT

[dao-jun]

Motivation

Use PulsarByteBufAllocator.DEFAULT instead of ByteBufAllocator.DEFAULT in FunctionsMetricsResource.

And this is for the purpose of unifying the memory allocation interface.

Modifications

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.23%. Comparing base (8559b68) to head (070bcfc).
⚠️ Report is 87 commits behind head on master.

Files with missing lines	Patch %	Lines
...ions/worker/rest/api/FunctionsMetricsResource.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #24952       +/-   ##
=============================================
+ Coverage     38.61%   74.23%   +35.61%     
- Complexity    13241    33884    +20643     
=============================================
  Files          1854     1913       +59     
  Lines        144861   149505     +4644     
  Branches      16804    17372      +568     
=============================================
+ Hits          55944   110982    +55038     
+ Misses        81409    29657    -51752     
- Partials       7508     8866     +1358     

Flag	Coverage Δ
inttests	26.46% <0.00%> (-0.05%)	⬇️
systests	22.76% <0.00%> (+0.01%)	⬆️
unittests	73.75% <0.00%> (+38.94%)	⬆️

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Files with missing lines	Coverage Δ
...ions/worker/rest/api/FunctionsMetricsResource.java	0.00% <0.00%> (ø)

... and 1416 files with indirect coverage changes

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