chore: Update ed25519-zebra to '4'

[jsantell]

Description

ed25519-zebra 3.1 is using a version of hashbrown that uses ahash that fails to build in rust nightly 1.78.0. Updating to edd25519-zebra >= 4 uses a newer version of hashbrown, and subsequently, ahash, that no longer has this issue.

ed25519-zebra recommends broadly targeting the major version "4".

cargo +nightly test now passes with this change.

Essentially a rebased #110

Link to issue

Please add a link to any relevant issues/tickets.

Type of change

The key types are public in ucan-key-support, so using both ucan-key-support and ed25519-zebra requires the two to be in sync.

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Refactor (non-breaking change that updates existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Comments have been added/updated

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (83528cc) 62.12% compared to head (97a269e) 62.33%.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
+ Coverage   62.12%   62.33%   +0.20%     
==========================================
  Files          24       24              
  Lines         895      884      -11     
  Branches      214      215       +1     
==========================================
- Hits          556      551       -5     
+ Misses        196      189       -7     
- Partials      143      144       +1     

see 13 files with indirect coverage changes