load, cache & show std replacements

[syphar]

TODO

• perhaps, if we can get a pure crate specific url for std replacements, can we drop the cache completely? and just live-fetch all the time per crate?

summary

Here we start showing crate warnings in the topbar.

First is the std-replacement data.
We're using a small partial so we can cache it independently from the rustdoc content.

For now, CDN caching is just a TTL of 10 minutes, with room for improvement.

We load the data from the json endpoint, which is properly cached through github pages.

For now we just run a scheduled task that updates the data every hour, happy to change the frequency.

first UI draft

First draft of the rendering, happy to take ideas? or help?

next steps

Idea is that I'll add rustsec "unmaintained" warnings as next thing, because they are relatively easy to interpret and also fit into the "crate warning" logic. In my mind I would show a second widget in the topbar if both warnings are raised by the same crate.

[syphar]

This is how crates.io renders the same warning:

Generally I feel like I want to find a way that we don't have to make the topbar bigger.

But not sure if this is worth a dropdown? or detail page like for the abnormalities?