Describe the bug
Very similar to #1615 but for msgspec.Struct output format

To Reproduce

Example schema:

openapi: 3.1.0
info:
  title: Bug report
  version: 0.0.1
paths:
  /api:
    get:
      responses:
        '200':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Model'
          description: ''
components:
  schemas:
    Model:
      type: object
      properties:
        updated:
          type: string
          format: date-time
        start:
          type: string
          format: date

Used commandline:

$ datamodel-codegen --input openapi.yaml --output models.py  --output-model-type msgspec.Struct --input-file-type openapi

Expected behavior

class Model(Struct):
    updated: Optional[datetime] = None
    start: Optional[date] = None

Instead right now they come out as str types.

Version:

• datamodel-code-generator version: 0.25.9

Additional context
Add any other context about the problem here.

I'm happy to attempt a PR if you'd like me to