refactor: Remove unused constraints

[matheus23]

Removes some unused constraints from type signatures:

• the ability type doesn't need Deserialize in Deserialize for Payload, because it actually uses ParseAbility::try_parse to parse, so ParseAbility is enough.
• Codec + TryFrom<u64> + Into<u64> is as good as Codec, because it's defined as trait Codec: [...] TryFrom<u64, Error = UnsupportedCodec> + Into<u64>.
• there was an unused <S as delegation::store::Store<...>>::DelegationStoreError: Debug constraint (it's part of the trait)
• I took the freedom to also make type InvocationStoreError: Debug in the invocation store, similar to the delegation store, and removed the constraints used elsewhere.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 13.09%. Comparing base (5dbd296) to head (88ce308).

Additional details and impacted files

@@              Coverage Diff               @@
##           v1.0-rc.1      #17       +/-   ##
==============================================
+ Coverage           0   13.09%   +13.09%     
==============================================
  Files              0       68       +68     
  Lines              0     5652     +5652     
  Branches           0     2709     +2709     
==============================================
+ Hits               0      740      +740     
- Misses             0     4316     +4316     
- Partials           0      596      +596     

Files	Coverage Δ
src/crypto/signature/envelope.rs	34.21% <ø> (ø)
src/crypto/varsig/header/eddsa.rs	15.38% <ø> (ø)
src/crypto/varsig/header/es256.rs	0.00% <ø> (ø)
src/crypto/varsig/header/es256k.rs	0.00% <ø> (ø)
src/crypto/varsig/header/es512.rs	0.00% <ø> (ø)
src/crypto/varsig/header/rs256.rs	0.00% <ø> (ø)
src/crypto/varsig/header/rs512.rs	0.00% <ø> (ø)
src/delegation.rs	100.00% <ø> (ø)
src/delegation/store/memory.rs	29.31% <ø> (ø)
src/delegation/store/traits.rs	60.00% <ø> (ø)
... and 5 more

... and 53 files with indirect coverage changes

[expede]

Yeah, there's probably a bunch of this as stuff shifted around. Thanks!