Implement `has` on `StoreGetXXX`

[maoueh]

Today we have StoreGet with the following definition:

pub trait StoreGet<T> {
    fn new(idx: u32) -> Self;
    fn get_at<K: AsRef<str>>(&self, ord: u64, key: K) -> Option<T>;
    fn get_last<K: AsRef<str>>(&self, key: K) -> Option<T>;
    fn get_first<K: AsRef<str>>(&self, key: K) -> Option<T>;
}

And then some specialized implementation of this trait like StoreGetProto that will automatically process the output and decode it to the specified proto message.

However, in some cases, we only care if a specific key is present like when implementing "dynamic data source" pattern on Ethereum. In those cases, we often don't need the actual data and we only want to determine if we should process the output of not.

This task is about adding fn has<K: AsRef<str>>(&self, ord: u64, key: K) -> bool support in StoreGet and for all concrete implementations. The method should only check if the key exists and avoid all decoding related to it.

• [x] Add support for has method on StoreGet (Add proper Rust documentation on the method has on the trait!).
• [x] Update the CHANGELOG.
• [x] Update substreams-uniswap-v3 to make use of this where it make sense.
• [ ] Maybe we should add a note on substreams CHANGELOG so this change is more discoverable

[colindickson]

@maoueh i propose to change the method name to has_at since it has essentially the same signature as get_at

[colindickson]

will be implementing has_at, has_first and has_last to mirror the get_ methods

[colindickson]

done on unstable