perf: keep fixed-width updates in place

[pathscale]

Summary

• stack directly on PR fix: revalidate vacuum links after row locking #54
• keep unindexed fixed-width field updates on the archived in-place path even when unrelated String columns make the row unsized
• remove unused UUID-v7 operation IDs from generated non-persistent update paths
• add deterministic codegen coverage and WTI/Congee/Arctic runtime coverage

Diagnosis

On PR #54 head, the supplied 10,000-operation probe measured:

• fresh insert: 17.99 ms
• old balance update: 45.66 ms (2.54x insert)
• old update after removing unused UUID generation: 34.20 ms (1.87x insert)
• corrected in-place update: 5.71 ms (0.30x insert)
• explicit delete plus insert: 33.97 ms

The delete-plus-insert result confirms that the old fixed-width update was accidentally taking the full-row reinsert path plus extra update bookkeeping.

Targeted validation

• codegen guard passed
• fixed-width update on an unsized row passed on WorkTablesIndex, Congee, and Arctic
• temporary wall-clock probes were removed and are not CI tests

Broader validation is deferred until the PR #54 CI repair is folded in.