Update experimental features in Astro 6 config

[twocaretcat]

Is an Issue Type Set?

• I've added an emoji to the issue title
• I've added a label to the issue (if possible)

What?

Update config for experimental features in astro.config.ts.

Tasks:

• Move the fonts config out of experimental since this API is now stable
• Enable experimental CSP
• Enable experimental Rust compiler
• Enable experimental queued rendering

Why?

The existing config is not compatible because some features have matured. Additionally, there are new experimental features which we can take advantage of.