Compile times

[nicoburns]

I've just been looking into compile times for Blitz. And read-fonts (16.14s) and skrifa (9.61s) both stand out in the profile. This is for a release build:

This mostly gets hidden by parallel compilation (the non-codegen times are not nearly so bad). And perhaps this is the only way to get the runtime performance and type safety of this crate. But nevertheless I though this should be tracked, and considered when implementing changes to these crates.

(note also the compile time for ttf-parser at the bottom of the screenshot - only 5.5s!)

[cmyr]

thanks! the codegen-based approach to the design of read-fonts does mean that we often end up compiling a lot of code, so naively I imagine that is most of what's going on here (and a quick look with -Ztime-passes doesn't show anything egregious). There are some design choices we could reconsider if this ends up feeling serious.