fix(tianmu): Fixup the mem leakage of aggregation function

[RingsC]

Summary about this PR

1: Fixup the memory leakage of aggregation function, which may lead to failed of malloc.
2: Re-impl the operator= of ValueOrNull.
3: Fixup the assertion of dow_cast in Query::ClearSubselectTransformation, Item_func_trig_cond.

Issue Number: close #1855

Tests Check List

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

Changelog

• New Feature
• Bug Fix
• Performance Improvement
• Build/Testing/CI/CD
• Documentation
• Not for changelog (changelog entry is not required)

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features

[mergify]

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[codecov]

Codecov Report

Patch coverage: 52.79% and project coverage change: +0.49 🎉

Comparison is base (2579bd4) 54.69% compared to head (2f16849) 55.18%.

❗ Current head 2f16849 differs from pull request most recent head 0ce0c57. Consider uploading reports for the commit 0ce0c57 to get more accurate results

Additional details and impacted files

@@                 Coverage Diff                 @@
##           stonedb-5.7-dev    #1867      +/-   ##
===================================================
+ Coverage            54.69%   55.18%   +0.49%     
===================================================
  Files                 2031     2031              
  Lines               431442   431521      +79     
===================================================
+ Hits                235965   238152    +2187     
+ Misses              195477   193369    -2108     

Impacted Files	Coverage Δ
storage/tianmu/common/common_definitions.h	84.21% <ø> (ø)
storage/tianmu/compress/basic_data_filt.cpp	45.03% <0.00%> (ø)
storage/tianmu/compress/data_stream.h	62.90% <ø> (ø)
storage/tianmu/compress/dictionary.h	26.61% <0.00%> (ø)
storage/tianmu/compress/inc_alloc.cpp	26.41% <ø> (ø)
storage/tianmu/compress/inc_alloc.h	6.66% <ø> (ø)
storage/tianmu/compress/inc_wgraph.cpp	2.19% <ø> (ø)
storage/tianmu/compress/inc_wgraph.h	5.88% <ø> (ø)
storage/tianmu/compress/ppm.cpp	0.00% <ø> (ø)
storage/tianmu/compress/suffix_tree.cpp	0.00% <0.00%> (ø)
... and 141 more

... and 146 files with indirect coverage changes

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[hustjieke]

LGTM