Add git commit hash tracking to library build

[moticless]

Summary

This PR adds automatic git commit hash tracking to the library build system, making it easier to identify which version of the code is running.

Changes

• Evaluate short 6-character git commit hash in src/lib/Makefile
• Pass commit hash as compile-time define via CFLAGS
• Add fallback to 'unknown' if git commit cannot be determined
• Log commit hash during parser finalization for version tracking

Example Output

INFO  : Finalizing parser configuration (commit: a70659)

This helps with debugging and support by clearly showing which git commit was used to build the library.

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Note

Low Risk
Small build/logging change with no parsing, auth, or data-path behavior changes.

Overview
The library build now bakes in a short git commit id at compile time and prints it when the parser finishes configuration.

src/lib/Makefile resolves a 6-character HEAD hash (or unknown outside git) and passes it via -DLIBRDB_GIT_COMMIT. parser.c defines a fallback macro and extends the existing finalize log line to include (commit: …).

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