msggen: Invoice.exposeprivatechannels override drops boolean variant from oneOf

[4xvgal]

The JSON schema for invoice.exposeprivatechannels defines a oneOf with both boolean and array variants (doc/schemas/invoice.json:63-83):

  "exposeprivatechannels": {
    "oneOf": [
      { "type": "boolean" },
      { "type": "array", "items": { "type": "short_channel_id" } },
      { "type": "short_channel_id" }
    ]
  }

However, in contrib/msggen/msggen/model.py:502, this field is manually overridden to only the array type:

  InvoiceExposeprivatechannelsField = ArrayField(
      itemtype=PrimitiveField("short_channel_id", None, None, added=None, deprecated=None),
      dims=1, path=None, description=None, added=None, deprecated=None
  )

And applied at model.py:544:

  overrides = {
      'Invoice.exposeprivatechannels': InvoiceExposeprivatechannelsField,
      ...
  }

This causes the generated cln-rpc binding to type the field as Option<Vec<ShortChannelId>> (cln-rpc/src/model.rs), making it impossible to pass exposeprivatechannels: true through the typed API.

Since msggen already has UnionField support for oneOf schemas (model.py:369-387), could this override be removed or updated to preserve both variants?