Avoid explicit cancellation in single-row cleanup - #2220

Summary

• stop explicitly calling IDbCommand.Cancel() from synchronous single-row query cleanup
• continue disposing the reader, command, parameters, and connection through the existing cleanup path
• add regression coverage for both zero-row and multiple-row QuerySingle failures

Root cause

QueryRowImpl explicitly cancelled an open reader whenever the method exited through an exception. This differs from QueryRowAsync, which relies on reader disposal. Some providers treat cancellation as a separate server operation; Oracle can surface ORA-01013 and obscure the meaningful zero-row or multiple-row exception.

Reader disposal is the provider-owned cleanup mechanism and keeps this path provider-neutral. Other command ownership paths, including unbuffered queries and QueryMultiple, are unchanged.

User impact

Single-row query failures retain their expected exception semantics without triggering provider-specific cancellation behavior. Resource cleanup remains intact.

Validation

• regression test verified red before the fix: both cases recorded an explicit cancellation
• targeted tests pass on net481, net8.0, and net10.0
• dotnet build Build.csproj -c Release /p:CI=true --no-restore succeeds
• full net10.0 test suite: 762 passed, 29 expected skips, 0 failed

Fixes #2215