Improve source file rendering speed

[Nemo157]

After deploying #1842 we have a few high spikes in the /crate/:name/:version/source/* 90th percentile response time

I was able to track down one of these from the access logs, https://docs.rs/crate/opus-sys/0.1.2/source/libopus/Makefile.in took 12.25s till first byte when I loaded it. It's surprisingly slow, https://docs.rs/crate/opus-sys/0.1.2/source/libopus/src/opus_encoder.c took <1s and is a similar size.

I'll try and find some time to look into it soon.

[syphar]

@Nemo157 do you think this is still an issue after the change to the other regex engine?

Looking at the 99th in grafana now I don't see any of these peaks any more?

[Nemo157]

Agreed this seems to be basically resolved, over the last week the highest spike was 1s