SPIKE: Investigate swapping in mrrc library for pymarc

[btravisebsco]

mrrc is a new rust MARC processing library, inspired by pymarc, with python bindings that may provide significant performance boosts to our MARC processing flows (~4x, possibly). We need to do some testing and evaluation of suitability.

• Create a branch of f_m_t
• Perform necessary refactoring (should be minimal) to swap in mrrc for pymarc
• Perform head-to-head testing

Watch out for:

• mrrc was largely a vibe-coding project built with Claude Code, so we need to do some due diligence on code quality
• Consider implementing an abstraction that allows mrrc to serve as an optional dependency