Add support for caching in build step

[joelhawksley]

Context

As documented in #96, we have observed a significant increase in ERB compilation overhead, which we see at boot time when using https://github.com/jhawthorn/actionview_precompiler and when ViewComponents compile their templates. On a test production deployment, we saw boot-time template precompilation jump from ~15s to nearly a minute, an unacceptable overhead to pay every time we boot a container.

Proposed solution

This PR adds a reactionview:precompile rake task that compiles all files covered by the Herb configuration inclusion/exclusion rules. If config.cache = true, the compiled cache is used, skipping the work of compiling ERB to Ruby. In a test production deployment we saw equivalent boot-time precompilation times in the 15s range.

If this change is generally deemed acceptable, I'd be happy to add docs to this PR.

Alternatives considered

Add cache to ActionView::Precompiler

I wrote jhawthorn/actionview_precompiler#46 (cc @jhawthorn) and deployed it to a lab environment with good results. However, the optimization is really only necessary for Herb, so adding the complexity there felt like a bit much.

Add cache to Herb

I wrote https://github.com/marcoroth/herb/compare/main...joelhawksley:herb:cache?expand=1 to add a cache to Herb instead. Unfortunately, ReActionView configures Herb with specific options which resulted in the cache not being hit.

Further opportunities

In a preliminary benchmark, I tried compiling to Ruby instruction sequences, resulting in performance faster than Erubi. I did not include this change here in order to keep things simple.

References

Closes #96

[marcoroth]

Thank you @joelhawksley! 🙏🏼

I want to be transparent here: I'll be at RubyKaigi next week and just added a mental note for this PR. I will get back to you after the conference, especially because I have some ideas I want to discuss with people to see if we actually need something like this. I'll keep you posted 🙌🏼