One stable math fuzz test

[elshan-eth]

Description

Added a fuzz test for stable matht to check that computeInvariant(balances) <= computeInvariant(balances + deltas)

Type of change

• Bug fix
• New feature
• Breaking change
• Dependency changes
• Code refactor / cleanup
• Optimization: [ ] gas / [ ] bytecode
• Documentation or wording changes
• Other

Checklist:

• The diff is legible and has no extraneous changes
• Complex code has been commented, including external interfaces
• Tests have 100% code coverage
• The base branch is either main, or there's a description of how to merge

Issue Resolution

[jubeira]

Thanks, this is looking good!

Let's just do the same test focusing on a smaller delta range, which is more prone to have issues. If balances increase too much, chances are the invariant will also increase significantly and that's also tested elsewhere; the question is more about possible manipulations around small deltas (even though in practice they'd hit other guardrails).

[jubeira]

LGTM, good finding! This makes sense.

We can now try a stateful test that checks the rate in a separate PR.