[chery-pick](branch-2.1) Pick "[Fix](group commit) Fix group commit block queue mem estimate fault"

[Yukang-Lian]

Pick [Fix](group commit) Fix group commit block queue mem estimate faule #35314

Proposed changes

Issue Number: close #xxx

Problem: When group commit=async_mode and NULL data is imported into a variant type column, it causes incorrect memory statistics for group commit backpressure, leading to a stuck issue. Cause: In group commit mode, blocks are first added to a queue in batches using add block, and then blocks are retrieved from the queue using get block. To track memory usage during backpressure, we add the block size to the memory statistics during add block and subtract the block size from the memory statistics during get block. However, for variant types, during the add block write to WAL, serialization occurs, which can merge types (e.g., merging int and bigint into bigint), thereby changing the block size. This results in a discrepancy between the block size during get block and add block, causing memory statistics to overflow.
Solution: Record the block size at the time of add block and use this recorded size during get block instead of the actual block size. This ensures consistency in the memory addition and subtraction.

Further comments

If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...

Proposed changes

Issue Number: close #xxx

[Yukang-Lian]

run buildall

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[doris-robot]

TeamCity be ut coverage result:
Function Coverage: 36.32% (9151/25194)
Line Coverage: 27.86% (74703/268115)
Region Coverage: 26.74% (38512/144033)
Branch Coverage: 23.45% (19521/83252)
Coverage Report: http://coverage.selectdb-in.cc/coverage/c01253eb4b4d2ffd8b1987dda27c81fb7464124f_c01253eb4b4d2ffd8b1987dda27c81fb7464124f/report/index.html