feat: concurrently load & parse fonts

[Itsusinn]

This will reduce load time from 2376ms to 388ms when loading many huge fonts

[Itsusinn]

@jackpot51 Could you please take a look?

[Itsusinn]

https://docs.rs/rayon-core/1.12.1/rayon_core/index.html#global-fallback-when-threading-is-unsupported

~~I just find rayon supports no_std, maybe it's unnecessary to add rayon feature-gate?~~

[CryZe]

That's not the same as no_std. If the crate doesn't have a std feature (and otherwise uses std features), then it doesn't support no_std.

[Itsusinn]

That's not the same as no_std. If the crate doesn't have a std feature (and otherwise uses std features), then it doesn't support no_std.

Understood