Function
increment
Atomically increment the value associated with the key in the store by the given (signed)
delta, returning the new value. A negative delta decrements, where decrement is just a
negative increment, rather than wasi:keyvalue's unsigned-only counter.
If the key does not exist in the store, it creates a new key-value pair with the value set to the given delta.
If any other error occurs, it returns an err(error).