Add `w4 check` to check if a cart is valid for WASM-4
WASM runtimes have different feature-sets.
Notably, wasm3 (the runtime used by WASM-4 native) doesn't support everything, but we also can't simply switch runtime completely (to something like Wasmer) since that would make WASM-4 less portable for embedded systems. Supporting multiple runtimes is good, but we have to stick to a feature-set they all accept.

For this reason, a command like `w4 check` which checks that a WASM file only uses opcodes and sections that all runtimes supports, and doesn't try to import things outside of the WASM-4 interface, could be useful.

This WASM functionality could also be useful for things like, for example, storing game metadata (`w4 meta`) or stripping unnecessary exports (`w4 cleanup`).