[x/programs] Change the state's put and delete methods to handle batches on the host

[richardpringle]

Where we can, we should avoid going in and out of the wasm-context. There should always be the option to batch calls.

Further, I think a single method for updates and deletes would be beneficial. Ideally, we could use something like

#[derive(BorshSerialize)]
struct CacheEntry<K> {
    key: K, 
    value: CacheValue,
}

#[derive(BorshSerialize)]
enum CacheValue {
    Get(Vec<u8>),
    Update(Vec<u8>),
    Delete,
}

I also think we would further benefit from

[derive(BorshSerialize)]
enum Update<K> {
    Put(K, Box<dyn BorshSerialize>),
    Delete(K),
}

where we could defer the actual serialization. It might be trickier to downcast the Box<dyn BorshSerialize> to a Box<T> when fetching from the cache though...