[Protobuf Schema] Map Field Handling in Composed Schemas

[lucy66hw]

This PR addresses a corner case where a map defined within an composed schema is being ignored during Protobuf generation.
Previously, the pet map (the field defined via additionalProperties) was not being handled properly, resulting in its omission from the generated proto file. the schema like the following:

schemas:
      Dog:
         allOf:
            - $ref: '#/components/schemas/DogBase'
            - type: object
              additionalProperties:
                 title: pet
                 $ref: '#/components/schemas/Pet'
              minProperties: 1
      Pet:
        type: string
      DogBase:
         type: object
         properties:
            bark:
               type: boolean
            breed:
               type: string
               enum: [ Dingo, Husky, Retriever, Shepherd ]

With this PR, the generator now correctly detects and processes the pet map, ensuring that it is included in the generated Protobuf message.

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[wing328]

can you please add some comments explaining what the code block does (e.g. what schema(s) it tries to handle) ?

[lucy66hw]

@wing328 thanks for reviewing the PR. I had added explaining comment on top of the code.