release-25.2: sql: don't run EXPLAIN ANALYZE via pausable portals

[yuzefovich]

Backport 1/1 commits from #155655.

/cc @cockroachdb/release

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This commit disables running EXPLAIN ANALYZE stmts via pausable portals model even if it's enabled. Previously, this led to a crash since different assumptions of how EXPLAIN ANALYZE is handled at the connExecutor level were broken, but it also doesn't make much sense to actually support this. After all, the result rows can only be produced after the query execution effectively completed, which contradicts the spirit of the pausable portal feature.

I briefly looked into making it work, but it doesn't seem worth it. There is a fundamental contradiction right now that we defer finishing the instrumentationHelper (which populates the output of EXPLAIN ANALYZE), and it currently happens after we close the commandResult in which we can write the output.

Fixes: #137597.

Release note (bug fix): Previously, CockroachDB would crash when executing EXPLAIN ANALYZE statements with the pausable portal model (meaning that it was run via the extended PGWire protocol using Parse, Bind, Execute, when multiple_active_portals_enabled session variable is enabled). The bug has been present since 23.2 and is now fixed.

Release justification: fix for a node crash.

[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. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. 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.

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

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[cockroach-teamcity]

This change is 

[blathers-crl]

✅ PR #155667 is compliant with backport policy

Confidence: high
Critical bug criteria met: [Stability or security issues]
Backward compatible: true
Explanation: The pull request backports a fix for a node crash issue, consistent with the critical bug criteria under the CockroachDB backport policy. A node crash is considered a stability issue, thus qualifying the change as addressing a critical bug. The PR description and the 'Release justification' explicitly mentions a crash caused by the 'pausable portal' feature, which is directly related to how 'EXPLAIN ANALYZE' statements were handled. Furthermore, none of the changes involve backward compatibility issues such as removal of version gates or break existing APIs. All changes are relevant to fixing the described issue without introducing features that require gating. Considering these factors, the PR is compliant with the backport policy.

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