Migrate the foreign method argument access API from an argument-oriented naming
scheme to a slot-based one, renaming wrenGetArgumentCount to wrenGetSlotCount,
wrenGetArgumentBool to wrenGetSlotBool, and all other argument accessors
accordingly. Update every call site across the VM, modules (io, timer, meta,
random), and test files (benchmark, foreign_class) to use the new names. The
slot getters now assert the correct type at runtime rather than silently
returning defaults, shifting safety responsibility to the caller for
performance. Also add the IS_LIST type-checking macro to wren_value.h alongside
the existing IS_* macros.
Add a new benchmark that measures the performance of calling foreign methods through the Wren C embedding API, specifically testing argument passing and return values with a tight loop of 10 million calls. Refactor test API classes from generic "Api" to specific names like "Call", "Returns", "Value", and "ForeignClass" to avoid naming conflicts with the new benchmark module. Update the benchmark runner to use the test_api executable for API-specific benchmarks and remove the special API test argument handling from the test runner.
