feat(cheatcodes): extend usable range in `assertApproxEqRel`

[beeb]

Motivation

For large values, the current implementation of the cheatcode assertApproxEqRel overflows during calculation of the relative delta. However, using a larger type for this calculation allows to prevent overflows and use the full range of uint256.

Solution

The calculation was modified to use U512 for the calculation and only check that the final value for the delta fits inside a uint256 (a requirement of the error type).

PR Checklist

• [x] Added Tests
• [ ] Added Documentation
• [ ] Breaking changes

[beeb]

@zerosnacks let me add an overflow test quickly, I noticed it's missing

[zerosnacks]

cc @klkvr would you mind double checking this proposed change