Fix matrix void method return lowering

[luisleo526]

What changed

• centralize the matrix mutators whose established C++ lowering returns void
• recognize terminal matrix mutators in namespace and member forms, emitting the mutation as a statement followed by the wrapper's default return
• preserve exact typed user-method precedence and namespace-shadowing behavior instead of classifying calls by method name alone
• add parser, analyzer, transpilation, native-compilation, mutator-form, and dispatch-collision regression coverage

Root cause

The terminal-expression classifier handled void drawing, array, and map calls, but not matrix mutators. A single-expression method ending in matrix.set(self, ...) or self.set(...) could therefore generate invalid C++ such as return self.set(...);, even though the runtime call returns void.

Matrix detection must also resolve the exact receiver type. Same-named authored typed methods take precedence over builtins and must remain returnable, including when a parameter named matrix shadows the builtin namespace.

Validation

• focused matrix void-method file: 25 passed; rerun after commit at the tested head
• focused receiver combination: 38 passed
• broader matrix/map/terminal regression suite: 282 passed
• full pytest: 2,500 passed, 1 skipped
• 685-source differential: 680 successes plus the same 5 established failures on baseline and candidate; zero status, diagnostic, or generated-C++ changes
• engine corpus: 252/252, fail=0; board 247 Excellent / 4 Strong / 1 documented anomaly; report regeneration and lock-step self-test passed
• 416-row scraper sweep: 409 OK, 1 no-trades, the same 5 transpile errors, 0 compile errors, the same 1 run error, 0 driver errors, and 0 unresolved timeouts
• final scraper board: 355 Excellent / 46 Strong / 4 Moderate / 2 Weak, plus 7 excluded; one patch-independent Strong-to-Excellent movement and zero DOWN
• tested head: 8f7dc924ed02696f2b799ec194c76187e3480bf6

The long gates ran against the exact three candidate file contents committed at the tested head. Their SHA-256 hashes were frozen before commit and verified unchanged after commit; the 25-case focused suite was then rerun from the clean committed head.

Scope boundary

This changes only terminal-call classification for matrix mutators whose existing C++ lowering returns void. It does not change the parser, analyzer, or matrix runtime implementations. remove_row and remove_col retain their existing numeric-sentinel lowering, and matrix-returning transforms remain on their established return path.