Add a 64-character maximum identifier length with compile-time error reporting, and enhance the runtime field overflow error to include the class name and remove the TODO comment. Update test expectations for both limit scenarios.
Add a MAX_FIELDS constant (255) to wren_common.h and implement field overflow
validation in the compiler and VM. The compiler now emits an error when a class
declares more than 255 fields, and the VM checks for inherited field overflow
at class creation time, producing a descriptive runtime error. Also add four
test files (many_fields, many_inherited_fields, too_many_fields,
too_many_inherited_fields) to verify both valid and invalid field counts.
