i'm not entirely happy with this hack tbh.

The next typst release will use `Duration` for offset; will have to address during upgrade so note is unnecessary.

- use Axum State instead of global OnceLock.
- make config module always return config for simplicity.
- add World to hold (and keep) constant state.
- move much of Context logic into World.
- use typst::World functions on Context to inject varying parameters: main file (template), inputs.
- set upload filename in main.
- miscellaneous lints.
- add build options.