Fix libparenth compatibility with fbitset c3ca474 (Size type change from int to size_t)

[Copilot]

• Identify the root cause of the build failure
• Fix the stream insertion operator template in test/matrixchain.cpp to match all three template parameters (Size N, typename L, typename E)
• Fix unsigned comparison bug in libparenth.hpp caused by fbitset Size type change from int to size_t
• Build and test the fix - all tests pass
• Update .gitignore to exclude build directory
• Untrack _codeql_build_dir and add to .gitignore

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[chenpeizhi]

@copilot You should untrack _codeql_build_dir and any other build artifacts.

[Copilot]

@copilot You should untrack _codeql_build_dir and any other build artifacts.

Done in commit 536fed7. Untracked _codeql_build_dir and added /_codeql_build_dir/ to .gitignore.