Add a new test framework for exercising the Wren C embedding API directly from C code, including a Makefile target, test runner modifications, and the first API test case for boolean return values. The build system now compiles test sources from `test/api/` into a separate test executable, and the CLI's `createVM` and `runFile` functions accept an optional `WrenBindForeignMethodFn` callback to enable foreign method binding in tests. The test runner (`script/test.py`) is refactored to support both script and API test types, passing the test name instead of the full path for API tests. The initial `return_bool` test verifies that `wrenReturnBool` correctly returns `true` and `false` from foreign methods.
Move runFile() and VM configuration logic from main.c into new vm.c module,
exposing createVM() and runFile() functions. This decouples CLI script
execution from the REPL and main entry point, enabling reuse of the same
VM setup and file-running code for API tests.
