Add executeInput() method to REPL that lexes input, determines if it's a statement or expression based on the first token, and evaluates accordingly using Meta.eval for statements or the new Meta.compileExpression for expressions. Extend Meta.compile_ foreign method with isExpression and printErrors parameters, update wrenCompile signature to support expression compilation mode, and add newline handling after equals in variable definitions.
Remove the `sourcePath` field from `FnDebug` struct and the `Parser` struct, and instead store it directly in `ObjModule`. This eliminates duplication of the debug path across all functions in a module and simplifies the compiler interface by removing the `sourcePath` parameter from `wrenCompile()` and `wrenNewFunction()`. Update all call sites to reference `module->sourcePath` instead, including stack trace printing, code dumping, and the `meta_eval` primitive.
Separate Wren VM library sources from CLI tool sources by moving them into
src/vm/ and src/cli/ subdirectories respectively. Update the Makefile to use
separate wildcard patterns for each directory, generate distinct object file
paths under build/vm/ and build/cli/, and adjust include paths to src/include.
Also update the Xcode project file to reference the new file locations.
