Rename CannotCidOr, API for creating powerlines & more

[matheus23]

• Renamed the associated types DelegationStoreError and InvocationStoreError into just Error. They're namespaced by the trait anyways, and is a common pattern in rust
• Renamed CannotCidOr to DelegationInsertError

Also, previously, given a delegation::Agent, there was no way to create a powerline. The Agent::signer is private, so it can't be used with Delegation::try_sign directly.
I get the fact that store.get_chain shouldn't take a subject: Option<DID>, but I think Agent::delegate should.
I needed that to keep creating powerlines from the fission-server crate.

---

And more things:

• Made expiration optional (although we're still discussing)
• Refactored to use let-else in Envelope::try_from_ipld_envelope
• Fixed and made use of Envelope::varsig_encode (I needed some API for getting a byte representation of a UCAN, and I think that's probably the best function?)
• Created missing via and command functions for accessing those Payload fields

[codecov]

Codecov Report

Attention: Patch coverage is 36.36364% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 12.86%. Comparing base (53c49d2) to head (2ed32e3).

❗ Current head 2ed32e3 differs from pull request most recent head 7dec84c. Consider uploading reports for the commit 7dec84c to get more accurate results

Additional details and impacted files

@@              Coverage Diff              @@
##           v1.0-rc.1      #18      +/-   ##
=============================================
+ Coverage      12.77%   12.86%   +0.08%     
=============================================
  Files             68       68              
  Lines           5612     5620       +8     
  Branches        2698     2703       +5     
=============================================
+ Hits             717      723       +6     
- Misses          4302     4309       +7     
+ Partials         593      588       -5     

Files	Coverage Δ
src/delegation.rs	100.00% <ø> (ø)
src/delegation/store/memory.rs	29.31% <100.00%> (ø)
src/delegation/store/traits.rs	60.00% <100.00%> (ø)
src/invocation/store/memory.rs	63.63% <100.00%> (ø)
src/invocation/store/traits.rs	100.00% <100.00%> (ø)
src/invocation/agent.rs	36.36% <0.00%> (ø)
src/invocation/payload.rs	32.94% <0.00%> (-0.20%)	⬇️
src/crypto/signature/envelope.rs	35.89% <42.85%> (+1.68%)	⬆️
src/delegation/payload.rs	46.89% <18.18%> (-0.59%)	⬇️

... and 4 files with indirect coverage changes

[expede]

and is a common pattern in rust

Yeah makes sense. I really dislike having to do nested <<Foo as Bar> as Baz>::Error, and giving unique names gets around this. It's probably just worth biting the bullet on the line noise 😆

[expede]

Renamed CannotCidOr to DelegationStoreError

Given that this is really specific to insert, have you considered DelegationInsertError? If we end up needing more error types over time, it would be nice to keep them separate so that we don't have to handle impossible cases downstream.

[matheus23]

Renamed CannotCidOr to DelegationStoreError

Given that this is really specific to insert, have you considered DelegationInsertError? If we end up needing more error types over time, it would be nice to keep them separate so that we don't have to handle impossible cases downstream.

Yeah you're raising a good point. I'll rename it now.

[matheus23]

I made expiration optional in one of the commits. I know we're still discussing this, so unless that discussion comes to an end, we shouldn't merge this yet.

[matheus23]

Rebased onto the latest v1.0-rc1 state.

[expede]

🎉 Looks great!