Add MAX_PARAMETERS constant set to 16 and extend VM bytecode instructions CODE_CALL_11 through CODE_CALL_16 to support the new limit. Introduce compile-time error messages when parameter or argument count exceeds 16 in function definitions, method declarations, subscript calls, and regular method calls. Add new native fiber call stubs fn_call9 through fn_call16 and register them in the core initialization. Include comprehensive test coverage for 9-16 parameter functions and methods, plus error tests for exceeding the limit in all contexts.
Rename the `primitives.h` and `primitives.c` files to `wren_core.h` and `wren_core.c` respectively, reflecting the module's purpose of defining built-in classes and native methods. Update all includes, macro names (PRIMITIVE -> NATIVE, DEF_PRIMITIVE -> DEF_NATIVE, etc.), and function calls (wrenLoadCore -> wrenInitializeCore) across the codebase and Xcode project file to match the new naming convention.
