Do we want cargo insta snapshot tests for each RPC?

[teor2345]

Goals

I want to check for accidental changes to RPC responses.

Suggestion

We could take a snapshot of each RPC response, and make sure it hasn't changed in our tests.

This stops us accidentally breaking RPCs with unrelated state, mempool, or chain tip changes.

Example

We already use cargo insta snapshot tests for database format changes.

Here is some example code:

zebra/zebra-state/src/service/finalized_state/zebra_db/block/tests/snapshot.rs

Lines 202 to 204 in 41d240f

	let tip = state.tip();
	insta::assert_ron_snapshot!("tip", tip.map(Tip::from));

And the resulting snapshot:

zebra/zebra-state/src/service/finalized_state/zebra_db/block/tests/snapshots/tip@mainnet_2.snap

Lines 7 to 10 in 41d240f

	Some(Tip(
	height: 2,
	block_hash: "0002a26c902619fc964443264feb16f1e3e2d71322fc53dcb81cc5d797e273ed",
	))

And here is what a snapshot diff looks like:
https://github.com/ZcashFoundation/zebra/pull/3874/files#diff-aadf7c9252b61764f4ec695cab23b1c64dab2d768b0000676b71d5fe70838a53L16