feat(provider): MockProvider

[yash-atreya]

Motivation

Closes #1148

Solution

WIP

• Introduce MockLayer, MockProvider, Asserter.
• Mocked responses are pushed into the Asserter
• Asserter queue is FIFO
• MockProvider pops the Asserter to get the next response and deserializes it into response type.

e.g

let (provider, asserter) = ProviderBuilder::mocked();

asserter.push_success(21965802);
asserter.push_success(21965803);
asserter.push_err(TransportError::NullResp);

let response = provider.get_block_number().await.unwrap();
assert_eq!(response, 21965802);

let response = provider.get_block_number().await.unwrap();
assert_eq!(response, 21965803);

let err_res = provider.get_block_number().await.unwrap_err();
assert!(matches!(err_res, TransportError::NullResp));

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[mattsse]

what's missing here?

[mattsse]

makes sense,

maybe this would also be possible by mocking the transport, but this should cover most usecases