Add test helper function which stores a program and registers a user

[ameba23]

Now that we no longer have pre-registered accounts, in order to test signing we need to first store a program and register a user. To reduce boilerplate in our siging tests, this adds a test helper function which stores a default program and registers a user using that program.

I've also made a change to the get_sign_tx_data test helper function. It now takes the verifying key as an argument, rather than defaulting to DAVE_VERIFYING_KEY, and sets the block number to the current block number rather than defaulting to zero.

One unrelated thing i noticed: We have a test called signature_request_with_derived_account_works which looks to me like it doesn't test anything extra than our other signing tests - it is left over from when we had two different signing flows. Do yous think we can get rid of it?

entropy-core/crates/threshold-signature-server/src/user/tests.rs

Line 320 in 624b37d

async fn signature_request_with_derived_account_works() {

[HCastano]

LGTM.

For your question around signature_request_with_derived_account_works, the point of that one versus the other tests is that it's a happy path only test.

The ones ones afair test different failure conditions, so I didn't want to mix them up.