enhance: Add split_cluster_writer to support vshard/clustering compactor

[wayblink]

issue: #36446

[codecov]

Codecov Report

Attention: Patch coverage is 64.51613% with 77 lines in your changes missing coverage. Please review.

Project coverage is 81.46%. Comparing base (06b5e18) to head (baab16b).
Report is 41 commits behind head on master.

Files with missing lines	Patch %	Lines
...ternal/datanode/compaction/split_cluster_writer.go	63.44%	49 Missing and 4 partials ⚠️
internal/datanode/compaction/segment_writer.go	62.50%	14 Missing and 7 partials ⚠️
internal/datanode/compaction/compactor_common.go	66.66%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #36447      +/-   ##
==========================================
+ Coverage   72.53%   81.46%   +8.92%     
==========================================
  Files        1308     1312       +4     
  Lines      156263   189106   +32843     
==========================================
+ Hits       113351   154061   +40710     
+ Misses      37801    29868    -7933     
- Partials     5111     5177      +66     

Files with missing lines	Coverage Δ
...ternal/datanode/compaction/clustering_compactor.go	72.95% <100.00%> (+4.00%)	⬆️
internal/datanode/compaction/merge_sort.go	73.52% <100.00%> (+0.68%)	⬆️
internal/datanode/compaction/mix_compactor.go	76.47% <100.00%> (-1.56%)	⬇️
internal/storage/primary_key.go	70.76% <100.00%> (-2.60%)	⬇️
internal/datanode/compaction/compactor_common.go	83.83% <66.66%> (-2.44%)	⬇️
internal/datanode/compaction/segment_writer.go	74.72% <62.50%> (-5.59%)	⬇️
...ternal/datanode/compaction/split_cluster_writer.go	63.44% <63.44%> (ø)

... and 1191 files with indirect coverage changes

[wayblink]

rerun ut

[sre-ci-robot]

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