Rename the nullifier test module

[teor2345]

Motivation

I'm planning on adding a transparent tests module as part of #2231.

Solution

• Change a module name

Review

@oxarbitrage can review this tiny PR, it's not urgent.

Reviewer Checklist

• Code works?

[oxarbitrage]

I am ok with this change but another option to organize them and highlight the fact they are prop tests is maybe:

tests/prop/nullifier.rs
tests/prop/transparent.rs

This way if we ever want to do the same with unit tests we can use:

tests/vectors/nullifiers.rs
tests/vectors/transparent.rs

[teor2345]

I am ok with this change but another option to organize them and highlight the fact they are prop tests is maybe:

tests/prop/nullifier.rs
tests/prop/transparent.rs

This way if we ever want to do the same with unit tests we can use:

tests/vectors/nullifiers.rs
tests/vectors/transparent.rs

I'd like to make that change after we finish up the rest of the state work. Because we might need to change these tests from proptests to fixed test vectors as part of that work.