Adds an assets server to the demo worker, and reworks the existing asset
server to use the same code. There are a few simplifications to the code
due to some DX improvements working with R2 and caches. I also removed
the `HEAD` request from the assets server: i took a look at our logs and
it's not actually used at all.
This also fixes an issue where users could overwrite the contents of the
asset uploads bucket.
### Change type
- [x] `other`
Describe what your pull request does. If you can, add GIFs or images
showing the before and after of your change.
### Change type
- [x] `bugfix`
- [ ] `improvement`
- [ ] `feature`
- [ ] `api`
- [ ] `other`
### Test plan
1. Create a shape...
2.
- [ ] Unit tests
- [ ] End to end tests
### Release notes
- Fixed a bug with...
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Co-authored-by: alex <alex@dytry.ch>
