ordering: do not automatically resubmit mutable transactions

[AkashKumar7902]

Refs #22086

What changed

• Classify every possible transaction branch, including nested transactions, before retrying an ordering violation.
• Retry only transactions that are provably read-only.
• Return the original successful response for a potentially mutable transaction when its violation handler returns nil, avoiding a second execution.
• Cover selected and unselected writes, nested transactions, handler errors, and read-only retries.

Why

txnOrdering.Commit currently retries any successful response whose revision is older than the wrapper's previously observed revision when the violation handler returns nil. If either transaction branch can write, the first execution may already have applied a mutation. Replaying the body can duplicate writes or watch events, or choose a different branch after intervening state changes.

Both branches must be read-only before retrying because the transaction comparison may produce a different result on the next endpoint. The violation handler is still called first, and its errors are still returned unchanged.

Impact

Read-only transaction retry behavior is unchanged. Potentially mutable transactions are reported to the violation handler but are not automatically replayed after a successful response. This does not add or change any exported API.

Backport candidate: release-3.7 and release-3.6.

Testing

• Confirmed the new regression test fails with the upstream Commit implementation.
• git diff --check
• cd client/v3 && go test ./ordering -count=20
• cd client/v3 && go test -race ./ordering -count=1
• cd client/v3 && go test ./... -count=1
• cd client/v3 && go vet ./ordering
• Targeted golangci-lint for client/v3/ordering: 0 issues.

[kubernetes-prow]

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[kubernetes-prow]

Hi @AkashKumar7902. Thanks for your PR.

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