refactor!: remove moonlex and moonyacc from build system

[peter-jerry-ye]

Summary

• remove moonlex and moonyacc binary wiring and special RR prebuild nodes
• stop recognizing .mbl/.mby as package source kinds
• hard-break legacy lexer/parser files with an explicit discovery error and migration hint to pre-build
• remove watch/test hooks and obsolete prebuild moonlex fixtures

Validation

• cargo fmt
• cargo check -p moon -p moonutil -p moonbuild-rupes-recta -p moonbuild-debug
• cargo test -p moonutil watch_relevant_project_file_covers_sources_and_manifests
• cargo test -p moonutil package_source_file_kind_detects_supported_package_inputs
• cargo test -p moon rerun_triggered_for_moon_pkg_dsl
• cargo test -p moon rr_get_prebuild_watch_paths_collects_inputs_and_outputs
• cargo test -p moon --test mod --no-run

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/moon/tests/test_cases/mod.rs	17% smaller
crates/moonbuild-rupes-recta/src/model.rs	9% smaller
crates/moonbuild-rupes-recta/src/build_plan/builders.rs	9% smaller
crates/moonutil/src/common.rs	1% smaller
crates/moon/src/watch/mod.rs	0% smaller
crates/moon/src/watch/prebuild_output.rs	0% smaller
crates/moon/tests/test_cases/prebuild/mod.rs	0% smaller
crates/moon/tests/test_cases/prebuild/moonlex/.gitignore	Unsupported file format
crates/moon/tests/test_cases/prebuild/moonlex/README.md	Unsupported file format
crates/moon/tests/test_cases/prebuild/moonlex/moon.mod.json	0% smaller
crates/moon/tests/test_cases/prebuild/moonlex/src/main/fortytwolexer.mbl	Unsupported file format
crates/moon/tests/test_cases/prebuild/moonlex/src/main/main.mbt	Unsupported file format
crates/moon/tests/test_cases/prebuild/moonlex/src/main/moon.pkg.json	0% smaller
crates/moonbuild-rupes-recta/src/build_lower/context.rs	0% smaller
crates/moonbuild-rupes-recta/src/build_lower/lower_aux.rs	0% smaller
crates/moonbuild-rupes-recta/src/build_plan/constructor.rs	0% smaller
crates/moonbuild-rupes-recta/src/discover/mod.rs	0% smaller
crates/moonbuild-rupes-recta/src/discover/model.rs	0% smaller
crates/moonbuild-rupes-recta/src/discover/synth.rs	0% smaller
crates/moonbuild-rupes-recta/src/util.rs	0% smaller
crates/moonutil/src/binaries.rs	0% smaller

[chatgpt-codex-connector]

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Reviewed commit: 7b23304799

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[chatgpt-codex-connector]

Keep legacy extensions watch-relevant in watch mode

Returning None for .mbl/.mby here makes is_watch_relevant_project_file ignore those files, while discovery now hard-fails with UnsupportedLegacyGeneratedSource when they exist. In moon --watch, adding a legacy file after a successful run will not trigger a rerun, so the watch session can keep showing stale success until another relevant file changes. That hides a real build-breaking state and undermines the intended immediate deprecation signal.

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