Increase regex timeout headroom for SQL refs

[Widthdom]

Summary

• Increase the bounded regex default timeout from 250 ms to 1 second so SQL reference extraction has more scheduler headroom under full-suite CPU contention.
• Add a focused regression guard for the bounded regex timeout budget.

Root Cause

Regex timeouts are treated as no-match fallbacks. Under heavy test-suite load, the previous 250 ms budget could intermittently turn SQL reference matches into missing references.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release --no-restore -p:UseSharedCompilation=false --filter "FullyQualifiedName~BoundedRegexTests|FullyQualifiedName~Extract_SQL_CreateIndexCapturesOnTableReference|FullyQualifiedName~RunReferences_ExactJson_SqlMergeTempTargetWithoutIntoResolvesTargetAndSource|FullyQualifiedName~RunReferences_ExactJson_SqlNonAsciiBareIdentifiersStayWhole|FullyQualifiedName~RunReferences_ExactJson_SqlMultilineSingleQuotedStringsStayOpaque"
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet format CodeIndex.sln --verify-no-changes --no-restore
• dotnet build CodeIndex.sln -p:UseSharedCompilation=false --no-restore
• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false --no-restore
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json

Full dotnet test CodeIndex.sln --no-restore -p:UseSharedCompilation=false was attempted locally but did not produce a final summary before being stopped, so it is not counted as a passing validation.

Documentation / Changelog

• Added changelog.d/unreleased/2949.fixed.md.
• No README or guide updates required; this only changes the bounded regex execution budget.

Fixes #2949