Load codehilite.css faster (cache headers, file name hash cache-busting)

[evnchn]

Motivation

While working on #5493 I also noticed that, full cached, NiceGUI documentation reaches out to:

• index.html (obviously)
• codehilite.css

The latter we should be able to get rid of?

Implementation

• Filename may change so we do ${this.filename} with the accompanying props.
• Compute the file name and return the response using _generate_codehilite_css(), which is shared.
• (Questionable) Apply @lru_cache(maxsize=1) to _generate_codehilite_css() because it doesn't ever change in runtime (an asusmption, is this right?)

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• The implementation is complete.
• Pytests have been added (or are not necessary).
• Documentation has been added (or is not necessary).

Results

Slow 4G no CPU throttling (because network is the bottleneck)

Before: 1.46s load
After: 1.00s load

[falkoschindler]

Thanks, @evnchn!

It took a while until I understood the need for the hash. First I thought we only need this single line:

headers={'Cache-Control': core.app.config.cache_control_directives},

But we need a way to change the content of this file in upcoming NiceGUI versions, so the URL shouldn't be fixed.

(Would it be possible/reasonable to move it into /_nicegui/<version>/?)

Anyway, the PR looks good as it is. We can think about further optimizations later.

[evnchn]

Would it be possible/reasonable to move it into /_nicegui//

Probably not, since we don't know what combo of library the user has installed (could be super out of date or extremely recent)

Yeah let's leave this PR as it is for now...