test: align PB memory leak check with RecordSet lifecycle

[zanmato1984]

Role: Coder-R251

Problem

The PB memory leak coverage checks post-read memory behavior around a result-set lifecycle, but the test was not closing the result set before making the final memory assertions. That leaves the coverage misaligned with the intended cleanup contract.

Root Cause

RecordSet.Close() is part of the expected lifecycle contract here. Reaching EOF is not the same thing as reaching lifecycle end: the lower-level response resource is already released at EOF, but the higher-level record-set / executor state is only cleared when Close() / Finish() runs. A local timing-window validation around that boundary substantially confirmed that this is the decisive boundary for the memory symptom exercised by the test.

Fix

Update TestPBMemoryLeak to assert a single result set, drain it, defer RecordSet.Close(), and only then run the post-read memory assertions.

Validation

• env GOCACHE=/tmp/go-build-omar go test --tags=intest,deadlock ./pkg/executor/test/unstabletest -run ^TestPBMemoryLeak -count=1
• env GOCACHE=/tmp/go-build-omar go test --tags=intest,deadlock ./pkg/executor/test/unstabletest -run ^TestPBMemoryLeak -count=5
• A local timing-window validation around the EOF-before-Close boundary repeatedly showed the memory symptom before Close() and its collapse after Close().

Scope

This strongly validates Close() as the decisive boundary for the memory symptom covered by this test. It does not overclaim universal certainty for every historical fluctuation outside this validated path.

[zanmato1984]

Role: Coder-R251

Rewrote the single PR commit with DCO signoff and force-with-lease pushed the branch to clear the DCO gate for fresh review.

[zanmato1984]

Role: Reviewer-R1

Verdict: LGTM

Checks performed:

1. Lifecycle boundary correctness: confirmed the test now closes the RecordSet before post-read memory assertions, matching the cleanup contract.
2. Result-set handling safety: verified a single-result expectation is asserted before indexing (require.Len(records, 1)).
3. Resource-release guarantee: verified record.Close() is deferred in a bounded closure, covering normal EOF and fail-fast paths.
4. Assertion validity after refactor: confirmed row-count validation still executes and memory assertions still verify allocation growth plus post-read in-use stabilization.
5. Scope/regression check: change is isolated to one unstable test file and does not alter production code paths.
6. PR hygiene and CI: verified DCO signoff on the commit and all required GitHub checks passing on this head SHA.

No material blocking issues found in the current PR state.

Note: GitHub does not allow approving your own PR from this account, so this is posted as a review comment rather than an approval event.