Skip unchanged current execution updates

[ali-khokhar-nvidia]

Fixes #11710.

What changed?

After locking and validating a current-execution row, SQL persistence now skips UpdateCurrentExecutions when every persisted field is already equal. Start times are compared at the microsecond precision used by the SQL type converters.

Why?

The existing path rewrites current_executions even when the desired row is unchanged. Avoiding that physical update removes unnecessary WAL and tuple churn while retaining the existing FOR UPDATE lock and run-ID validation.

How did you test it?

• built
• run locally and tested manually
• covered by existing tests
• added new unit test(s)
• added new functional test(s)

go test ./common/persistence/sql -run '^Test(CurrentExecutionsEqual|AssertRunIDAndUpdateCurrentExecutionSkipsUnchangedRow)$' -count=1

The tests cover every field in CurrentExecutionsRow, verify database timestamp precision, prove an identical row performs zero updates, and prove a changed field still performs one update.

Potential risks

Only semantically identical rows skip the update. Changed state, status, identity, version, payload, encoding, or timestamp values continue through the existing update path.

[CLAassistant]

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