Make nullifier tests faster and consistent with UTXO tests

[teor2345]

Motivation

The nullifier tests are a bit slow on some developers' machines.

This PR also makes minor changes to the nullifier test code to match the UTXO tests in PR #2511.

This PR does not close any tickets.

Solution

• reduce the number of proptest cases for slow state tests
• rename tests for consistency and clarity
• make some non-finalized state methods test-only

Review

@oxarbitrage can review this PR. It's not urgent at all.

Reviewer Checklist

• Refactors make sense
• Tests are faster

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This change is 

[oxarbitrage]

Reviewed 4 of 4 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @teor2345)

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zebra-state/src/service/non_finalized_state/tests/prop.rs, line 17 at r1 (raw file):

};

const DEFAULT_PARTIAL_CHAIN_PROPTEST_CASES: u32 = 16;

I think it will be good to change this one as well: https://github.com/ZcashFoundation/zebra/blob/main/zebra-state/src/service/non_finalized_state/tests/prop.rs#L17 but we can do it in a separated PR.

[oxarbitrage]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @teor2345)

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zebra-state/src/service/non_finalized_state/tests/prop.rs, line 17 at r1 (raw file):

Previously, oxarbitrage (Alfredo Garcia) wrote…

I think it will be good to change this one as well: https://github.com/ZcashFoundation/zebra/blob/main/zebra-state/src/service/non_finalized_state/tests/prop.rs#L17 but we can do it in a separated PR.

Sorry, i posted the link for the one changed. I wanted to say to make an additional change here: https://github.com/ZcashFoundation/zebra/blob/main/zebra-state/src/service/finalized_state/tests/prop.rs#L15

[oxarbitrage]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @teor2345)

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zebra-state/src/service/non_finalized_state/tests/prop.rs, line 17 at r1 (raw file):

Previously, oxarbitrage (Alfredo Garcia) wrote…

Sorry, i posted the link for the one changed. I wanted to say to make an additional change here: https://github.com/ZcashFoundation/zebra/blob/main/zebra-state/src/service/finalized_state/tests/prop.rs#L15

I opened a PR for this at #2521

[oxarbitrage]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @teor2345)