Add other types to pydantic (#2274)

Adds support for Pdf, Video and Audio.
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> [!IMPORTANT]
> Add support for Pdf, Video, and Audio types in Pydantic models with
corresponding tests.
> 
>   - **Behavior**:
> - Adds support for `Pdf`, `Video`, and `Audio` types in Pydantic
models.
> - Updates `__get_pydantic_core_schema__()` in `media_repr.rs` to
handle new media types.
>   - **Tests**:
> - Adds `test_pydantic_audio.py` to test `Audio` type serialization and
deserialization.
> - Adds `test_pydantic_pdf.py` to test `Pdf` type serialization and
deserialization.
> - Adds `test_pydantic_video.py` to test `Video` type serialization and
deserialization.
>   - **Misc**:
> - Refactors `_union_schema()` in `media_repr.rs` for cleaner schema
definition.
> 
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Author: egol