Fix data branch decimal results on main

[gouhongshen]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #24847

What this PR does / why we need it:

Port the data branch decimal result conversion fix to main.

• Preserve decimal precision/scale metadata from MySQL result columns and validate invalid/missing decimal metadata.
• Materialize decimal64/decimal128/decimal256 row values as typed MatrixOne vectors when building data branch output batches.
• Decode and compare decimal256 raw tuple values in data branch hashdiff/change replay paths.
• Add focused unit tests and BVT coverage with diff_14.sql for decimal64/decimal128/decimal256 data branch diff.

Notes:

• The pick subquery string-literal fix from 565a0f71 is already present in main with tree.WithSingleQuoteString() and unit coverage.
• The decimal256 PK pick issue is tracked separately in [Bug]: data branch pick does not support decimal256 primary keys #24902 and intentionally not fixed in this PR.

Checks:

• make -C thirdparties
• source $HOME/.zshrc && moenv && go test ./pkg/container/types ./pkg/frontend ./pkg/vm/engine/disttae/logtailreplay
• git diff --check upstream/main...HEAD

Draft until CI confirms this port on main.

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