fix(repl): avoid cloning the global name map on feed

[tristanang]

Summary

• mutate the REPL global name map in place during incremental prepare instead of cloning it for each feed/start
• remove the old incremental name-map commit path and keep only intern/function metadata commits after execution
• add regression tests covering compile-time failures that reserve a global slot before erroring

Testing

• make install-py
• make format-rs
• make lint-rs
• cargo test -p monty --test repl

fixes #249

[codecov]

Codecov Report

❌ Patch coverage is 33.60656% with 81 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/monty/src/repl.rs	35.22%	27 Missing and 30 partials ⚠️
crates/monty/src/prepare.rs	29.41%	20 Missing and 4 partials ⚠️

📢 Thoughts on this report? Let us know!

[codspeed-hq]

Merging this PR will not alter performance

✅ 13 untouched benchmarks

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_{Comparing tristanang:t3code/fix-monty-issue-249 (1632a02) with main (e59c8fa)}