float: Replace some approximate assertions with exact
As was mentioned at [1], we currently use `assert_approx_eq` for testing
some math functions that guarantee exact results. Replace approximate
assertions with exact ones for the following:
* `ceil`
* `floor`
* `fract`
* `from_bits`
* `mul_add`
* `round_ties_even`
* `round`
* `trunc`
This likely wasn't done in the past to avoid writing out exact decimals
that don't match the intuitive answer (e.g. 1.3 - 1.0 = 0.300...004),
but ensuring our results are accurate seems more important here.
[1]: https://github.com/rust-lang/rust/pull/138087#issuecomment-2842069281
The first commit is a small bit of macro cleanup.
try-job: aarch64-gnu
try-job: x86_64-gnu-aux
3ebdd59770