Extract Signature

[bh2smith]

Introducing Type Interface for TxStatus and a function to extract signatures with a unit test. Here is an example response from the RPC.

Special Notes

1. It is very strange to have to define types for RPC call responses. There should be a library maintaining these types... like near-rpc or something.
2. The near docs do not specify a type for this response data (merely an example response with empty arrays in the any fields). However, QuickNode does provide some vague documentation about these types (but their example still returns an empty array -- i.e. not enough to declare types). This issue is captured in a TODO comment (see inline changes), but does not affect the functionality of our code (cf passing CI).
3. The test introduced here is more of an integration test than a unit test (because it does call the testnet rpc).

cc @SurgeCode

⚠️ I HAVE TEMPORARILY DISABLED E2E tests in CI (because MPC Contract is currently not functional) ⚠️