Inline monomorphic methods in optimized Lua - #1296

Summary

• lower monomorphic method calls inside Lua hot loops to ordinary IM function calls before inlining
• reuse the backend's existing direct-call predicate in vararg lowering and final emission
• preserve callback, local-player, recursion, register-pressure, and genuine virtual-dispatch boundaries
• keep calls outside loops in their established representation to avoid broad code-shape churn

Acceptance criteria

• tiny monomorphic methods disappear from optimized Lua hot loops
• receivers are evaluated exactly once
• callback/function-reference and local-player-sensitive methods keep their call boundaries
• abstract/overridden and virtually dispatched vararg methods retain dispatch
• the existing UnitSpatialIndex loop still emits raw table accesses without assurance, vararg-pack, or arithmetic-helper overhead

Checks

• PASS: focused 10-test LuaBackendAuditTests matrix covering the new behavior, Jass/Lua receiver parity, callback and local-player barriers, fixed and dynamic varargs, virtual dispatch, and UnitSpatialIndex emitted shape
• PASS: complete LuaTranslationTests class (114 tests)
• PASS: GitHub Actions full Gradle build and test suite
• PASS: git diff --check

Review

• Codex review completed cleanly on head 4da675e9dc with no inline findings or unresolved threads.