Support for "long" number format #421

Hello! First of all thank you very much for this project, this is great!

I am working on using this tool to generate a client and types from an OAPI v3 spec that contains some number types with "long" format like this:

{
          "someNumberField" : {
            "type" : "number",
            "description" : "Some description.",
            "format" : "long",
            "example" : 100
          }
}

Currently this is throwing an error when I attempt to do generation:

error resolving primitive type: invalid number format: long

This appears to be a valid OAPI v3 number format, at least it passes validation here. So I was wondering if you would be open to adding it to the supported formats here.

I'd be more than happy to submit a PR for this if so!