fix: rename PanicError and fix executor OOM mapping

[sundy-li]

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Summary

Fixes #19612.

Rename ErrorCode::PanicError to ErrorCode::UnwindError while keeping error code 1104, and stop using that code for memory-limit flush failures in the pipeline executor.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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