SCORU: Wasm PVM: implement store_has

Goal

Implement the store_has host capability (see docs).

This allows a kernel to retrieve whether a given key exists in the durable storage.

The host function should be compatible with:

(module
  ...
  (type (;2;) (func (param i32 i32) (result i32)))
  ...
  (import "rollup_safe_core" "store_has" (func (;2;) (type 2)))
  ...