chore(tests): add fuzz test for rewards

[0x-r4bbit]

This fuzz tests keeps failing with:

Encountered 1 failing test in test/RewardsStreamerMP.t.sol:FuzzTests
[FAIL: assertion failed: 1726462282400621448432032544431078332388 !~= 1726462282400621448432032544431079957287 (max delta: 300, real delta: 1624899); counterexample: calldata=0xe14c93cc0000000000000000000000000000000000000000000681c3694c0b34a24b48300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000310b828f8452243d6cc3766de75e5153d600000000000000000000000000000000000000000000000000000000000002270000000000000000000000000000000000000000000000000000000000000039 args=[7866344896524125544859696 [7.866e24], 0, 16689135396539340668176314596167106253782 [1.668e40], 551, 57]] testFuzz_Rewards(uint256,uint256,uint256,uint16,uint16) (runs: 1, μ: 522606, ~: 522606)

The delta is way too big.
We're still dealing with a single staker.

Checklist

Ensure you completed all of the steps below before submitting your pull request:

• Added natspec comments?
• Ran pnpm adorno?
• Ran pnpm verify?