fix: Update nonce schema with IPLD bytes

[bgins]

Description

This PR makes the following changes:

• Update the nonce schema one of IPLD bytes or empty string
• Add workflow validation test that uses a nonce

The schema will be updated by the schemas action, but as a preview it looks like this:

"nnc": {
  "description": "A 12-byte or 16-byte nonce encoded as IPLD bytes. Use empty string for no nonce.",
  "oneOf": [
    {
      "$ref": "#/definitions/ipld_bytes"
    },
    {
      "type": "string",
      "const": ""
    }
  ]
},

"ipld_bytes": {
  "title": "IPLD bytes",
  "description": "Base64 encoded binary",
  "type": "object",
  "properties": {
    "/": {
      "type": "object",
      "properties": {
        "bytes": {
          "type": "string"
        }
      }
    }
  }
},

Type of change

• Bug fix (non-breaking change that fixes an issue)
• This change requires a documentation update (schemas will be updated by the action)

Test plan (required)

A new validate_and_parse_workflow_with_nonce has been added that validates a workflow with a task that uses a nonce.

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 72.40%. Comparing base (2d77b0a) to head (269f45f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #593      +/-   ##
==========================================
- Coverage   72.42%   72.40%   -0.02%     
==========================================
  Files          95       95              
  Lines       12473    12505      +32     
==========================================
+ Hits         9033     9054      +21     
- Misses       3440     3451      +11     

Files	Coverage Δ
homestar-runtime/src/runner/file.rs	96.59% <100.00%> (+1.00%)	⬆️
homestar-invocation/src/task/instruction/nonce.rs	52.27% <0.00%> (-8.26%)	⬇️

... and 1 file with indirect coverage changes