fix: Handle default values correctly during compaction for added fields

[congqixia]

Related to #45543

When a field with a default value is added to a collection, the default value becomes null after compaction instead of retaining the expected default value.

Root Cause The appendValueAt function in internal/storage/arrow_util.go incorrectly checked if the entire arrow.Array was nil before handling default values. This meant that default values were only applied when the array itself was nil, not when individual field values were null (which is the correct condition).

Changes

1. Early nil check: Added a guard at the function entry to detect nil arrow.Array and return an error immediately, as this is an unexpected condition that should not occur during normal operation.

2. Refactored default value handling: Removed the per-type nil array checks and moved default value logic to handle individual null values within the array (when IsNull(idx) returns true).

3. Applied to all types: Updated the logic consistently across all builder types:

   • BooleanBuilder
   • Int8Builder, Int16Builder, Int32Builder, Int64Builder
   • Float32Builder
   • StringBuilder
   • BinaryBuilder (added default value support for internal $meta json)
   • ListBuilder (removed unnecessary nil check)

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[codecov[bot]]

Codecov Report

:x: Patch coverage is 83.33333% with 6 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 76.48%. Comparing base (96d0e78) to head (dd78d05). :warning: Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/storage/arrow_util.go	83.33%	6 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #45572      +/-   ##
==========================================
- Coverage   76.55%   76.48%   -0.07%     
==========================================
  Files        1875     1875              
  Lines      291983   291953      -30     
==========================================
- Hits       223531   223307     -224     
- Misses      61073    61237     +164     
- Partials     7379     7409      +30     

Components	Coverage Δ
Client	78.17% <ø> (ø)
Core	83.18% <ø> (ø)
Go	74.59% <83.33%> (-0.11%)	:arrow_down:

Files with missing lines	Coverage Δ
internal/storage/arrow_util.go	72.55% <83.33%> (+11.46%)	:arrow_up:

... and 41 files with indirect coverage changes

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[congqixia]

/ci-rerun-ut-go

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@congqixia cpu-e2e job failed, comment /run-cpu-e2e can trigger the job again.

[congqixia]

/run-cpu-e2e

[congqixia]

/ci-rerun-ut-integration

[mergify[bot]]

@congqixia cpu-e2e job failed, comment /run-cpu-e2e can trigger the job again.

[congqixia]

/ci-rerun-ut-go

[congqixia]

/ci-rerun-ut-go

[congqixia]

/ci-rerun-ut-go

[congqixia]

/ci-rerun-ut-go

[tedxu]

/lgtm /approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: congqixia, tedxu

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