fix data branch no-op update diff

[gouhongshen]

What type of PR is this?

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

Which issue(s) this PR fixes:

Related to #23751

What this PR does / why we need it:

Fixes data branch diff reporting no-op updates after a row is updated and then restored to the LCA/snapshot value.

Root cause: findDeleteAndUpdateBat treated a tombstone plus a matching live row for the same PK as an UPDATE based only on PK matching. It did not compare the decoded replacement tuple with the LCA delete row, so rows whose visible values had returned to the LCA value still appeared in diff output.

Changes:

• Compare the decoded live tuple with the LCA row before emitting an UPDATE, and suppress the update when all visible non-PK values are equal.
• Reuse the existing vector comparison path by factoring value extraction/normalization helpers for vector-vs-vector and tuple-vs-vector comparison.
• Keep fake-PK tables conservative by comparing the full visible row.
• Add focused frontend unit tests for restored rows, real updates, and fake-PK behavior.
• Add git4data/branch/diff_14 BVT coverage for restored-update diffs and merge direction semantics.

Validation:

• ./run.sh -p /Users/ghs-mo/MOWorkSpace/matrixone-2nd/test/distributed/cases/ -m genrs -i diff_14
• ./run.sh -p /Users/ghs-mo/MOWorkSpace/matrixone-2nd/test/distributed/cases/ -i diff_14 - 58/58 passed
• CGO_CFLAGS="-I$PWD/cgo -I$PWD/thirdparties/install/include" CGO_LDFLAGS="-L$PWD/cgo -lmo -L$PWD/thirdparties/install/lib -Wl,-rpath,$PWD/lib" DYLD_LIBRARY_PATH="$PWD/lib:$PWD/cgo:$PWD/thirdparties/install/lib" go test ./pkg/frontend -run 'TestHashDiff_HasLCA|TestHashDiff_NoLCAWithStubHandles|TestDataBranchCompareSingleValInVector'

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