TimeSpan in response model ignored by generator

[llotall]

Describe the bug
TimeSpan type in backend response model doesn't generated on frontend model

To Reproduce

 "SomeResponse": {
        "type": "object",
        "properties": {
          "delay": {
            "type": "string",
            "format": "date-span"
          }
        },
        "additionalProperties": false
      }

Expected behavior
In forntend model generated property according to reponse property type