fontique: Remove unsafe in fontconfig cache

[waywardmonkeys]

Instead of transmuting the CharSetLeaf to the underlying value and then doing the operations on that, use the operation as already exposed via CharSetLeaf::contains_byte.

[waywardmonkeys]

I'm unable to test this locally, so some care should be exercised.

In #77, updating to Rust 1.79 enabled a new clippy lint about how transmute calls are annotated and instead of doing what it suggested, I thought it would be better to get rid of the transmute entirely instead.

One option was to just call font.coverage.leaves.push(leaf.map) instead of transmuting, since the map has the right type and is pub, so no transmute would be required.

That felt a bit odd though to do and I thought maybe this approach would be better since it would use the code that already exists within fontconfig-cache-parser.

Is there an issue with this not inlining that code? (If so, could flag that method in a future release of fontconfig-cache-parser as #[inline] perhaps?)

Or, going by my mental track record of late after illness, I could just be entirely wrong here.

[waywardmonkeys]

(Another option might have been to use even more code from fontconfig-cache-parser, but I don't know enough at that point about this and the requirements to be sure...)

[jneem]

Looks fine to me, although I'm not sure that I have approval authority.

[dfrg]

I can’t say why I didn’t structure the code this way originally but the change looks good to me. Thanks!