postgres: fix ERROR-level log spam from explain_parameterized_queries on type mismatch

[pierreln-dd]

What does this PR do?

Catch psycopg.errors.UndefinedFunction and psycopg.errors.DatatypeMismatch inside _explain_prepared_statement before they escape to the @tracked_method decorator. Log at DEBUG, return None as a sentinel. explain_statement maps None → DBExplainError.undefined_function so the failure remains observable in collection_errors telemetry.

Motivation

When explain_parameterized_queries: true is enabled and the agent runs EXPLAIN EXECUTE dd_X(null, ...) against a query that compares a non-text column to an untyped $N parameter, PostgreSQL raises UndefinedFunction (SQLSTATE 42883). This escaped _explain_prepared_statement to the @tracked_method decorator, which calls check.log.exception() at ERROR with no rate limiting — one ERROR per explain attempt per unique query signature.

The April 2025 PREPARE-phase fixes (#19969 / #19998) patched the same error classes in _create_prepared_statement but left the EXECUTE phase unpatched. This PR closes that gap.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add qa/required if this PR needs QA validation, or qa/skip-qa if it does not. Exactly one of the two is required.
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[datadog-datadog-prod-us1-2]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 94.44%
• Overall Coverage: 94.07% (+6.35%)

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[dd-octo-sts]

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