This fixes #599

With the changes in this pull request, the following OpenAPI document:

openapi: '3.0.1'
paths:
  '/t/foo/{id}':
    get:
      operationId: getFoo
      parameters:
        - name: id
          in: path
          required: true
          format: int64
          type: integer
        - name: valid_from
          in: query
          required: true
          format: date
          type: string
        - name: valid_to
          in: query
          required: true
          format: date
          type: string
        - name: test_time
          in: query
          required: true
          format: time
          type: string
        - name: test_datetime
          in: query
          required: true
          format: date-time
          type: string
      responses:
        '200':
          description: No response was specified

generates the following Refit interface:

[Get("/t/foo/{id}")]
Task GetFoo(
    long id, 
    [Query(Format = "yyyy-MM-dd")] System.DateTimeOffset valid_from, 
    [Query(Format = "yyyy-MM-dd")] System.DateTimeOffset valid_to, 
    [Query] System.TimeSpan test_time, 
    [Query] System.DateTimeOffset test_datetime);

This pull request includes changes to the Refitter project, focusing on improving date handling and updating test cases. The most important changes include modifying the date format handling in ParameterExtractor.cs, updating test cases to reflect these changes, and converting the OpenAPI specification format from JSON to YAML.

Improvements to date handling:

• src/Refitter.Core/ParameterExtractor.cs: Modified the switch case to handle IsDate separately from IsDateOrDateTime when UseIsoDateFormat is true.

Updates to test cases:

• src/Refitter.Tests/Examples/UseIsoDateFormatTests.cs: Updated the OpenAPI specification format from JSON to YAML.
• src/Refitter.Tests/Examples/UseIsoDateFormatTests.cs: Added new test cases to check for the presence and absence of specific date format strings in the generated code.
• src/Refitter.Tests/Examples/UseIsoDateFormatTests.cs: Simplified the GenerateCode method by combining settings initialization into a single line.
• src/Refitter.Tests/Examples/UseIsoDateFormatTests.cs: Changed the file extension for the generated Swagger file from .json to .yaml.