Implement typed header parsing for ucan header

[cdata]

After we integrate support for changes to rs-ucan landing in ucan-wg/rs-ucan#28, we will have to contend with a new world where HTTP request headers that use UCAN-based JWT for authorization may also include auxilliary ucan headers (see: https://github.com/ucan-wg/ucan-as-bearer-token#2-request-headers).

We already benefit from typed header parsing for the authorization header. We should author an extension to the typed headers that are offered by axum to include something to make parsing ucan headers more convenient and consistent.

[blaine]

If anyone looks to pick this up, we have [almost] an implementation in fission-server that will be extracted to a generic axum extractor. Will update as we get closer. It probably makes sense to implement this as a separate crate from rs-ucan, but appreciate any thoughts on the matter!

ucan-wg/rs-ucan#122

[jsantell]

Implemented: https://github.com/subconsciousnetwork/noosphere/blob/main/rust/noosphere-core/src/api/headers/ucan.rs