test(extraction): regression guards for #382 (Java annotations) + #213 (large TS)

#382 — Java Method nodes now carry decorators (@GetMapping) and a non-empty
signature; verified by extract_java_method_annotations_issue382.
#213 — a 256 KB / 4000-function TS file now yields Function nodes instead of
a childless File node (fixed by the tree-sitter read-buffer padding);
verified by extract_large_ts_has_functions_issue213.

Closes #382. Closes #213.