release-25.4: kvserver: stop treating split/merge trigger errors as replica corruption

[tbg]

Backport 1/1 commits from #167289.

/cc @cockroachdb/release

---

Previously, maybeWrapReplicaCorruptionError in RunCommitTrigger
escalated any unrecognized error from split/merge trigger evaluation to
a ReplicaCorruptionError, which crashes the process via
setCorruptRaftMuLocked. This meant that transient I/O errors (e.g.
cloud storage network timeouts during MVCCIsSpanEmpty) would fatal
the node despite not indicating actual data corruption.

Remove the corruption wrapping so that these errors simply fail the
split or merge, which will be retried.

This is a minimal fix suitable for backporting. Follow-up work can
remove the now-no-op maybeWrapReplicaCorruptionError wrapper entirely.

Fixes-26.2: #165558
Epic: CRDB-61447

Release note (bug fix): Fixed a bug where transient I/O errors (such
as cloud storage network timeouts) during split or merge trigger
evaluation were misidentified as replica corruption, causing the node
to crash. These errors now correctly fail the operation, which is
retried automatically.

Release justification: bug fix: transient I/O errors during split/merge incorrectly crash the node

[trunk-io]

😎 Merged successfully - details.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes OR fixes for serious issues. Non-production includes test-only changes, build system changes, etc. Serious issues are defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to. Reference the approved ENGREQ ticket in the PR body (e.g., "Fixes ENGREQ-123").

Add a brief release justification to the PR description explaining your selection.

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[cockroach-teamcity]

This change is