with c-m-i-n, the contract would be:

- PAC must define exactly one enum implementing `InterruptNumber`, where
  - The value of the variant must be the interrupt number
  - The name of the variant must be the symbol name
- PAC must define a `device.x` defaulting all interrupts to DefaultHandler
- PAC must define a `#[link_section = ".vector_table.interrupts"] #[no_mangle] pub static __INTERRUPTS = ...`