[eisen0419]

Related Issue: Fixes #213

Type of change:

• Bug fix (non-breaking change which fixes an issue)

Description:
Both Pydantic CloudEvent implementations (cloudevents.v1.pydantic.v2.event and cloudevents.v1.pydantic.v1.event, re-exported via cloudevents.v1.pydantic.CloudEvent) serialize structured JSON through cloudevents.v1.conversion.to_json, which delegates to stdlib json.dumps without applying Pydantic's JSON serializer to data. As a result, calling .json() or .model_dump_json() when data contains datetime (or other Pydantic-serializable types such as date, time, UUID, Decimal, or nested BaseModel instances) raised TypeError: Object of type datetime is not JSON serializable.

This change encodes non-binary data payloads with the corresponding Pydantic serializer prior to conversion.to_json while leaving top-level binary payloads (bytes, bytearray, memoryview) untouched so they continue to serialize as data_base64 per the CloudEvents JSON format specification:

• Pydantic v2: encodes non-binary data via TypeAdapter(Any).dump_python(..., mode="json") while forwarding relevant SerializationInfo options (by_alias, exclude_unset, exclude_defaults, exclude_none, exclude_computed_fields, round_trip, serialize_as_any, polymorphic_serialization, context).
• Pydantic v1: encodes non-binary data using the default encoder passed into Config.json_dumps (including custom json_encoders and .json(encoder=...)) while preserving outer json.dumps formatting arguments.
• Envelope attributes (time RFC3339 formatting, null-attribute omission, extensions) and event.data in-memory values remain unchanged.

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Pre-submission checklist:

• I have read the CONTRIBUTING.md file.
• I have signed off my commits using git commit --signoff.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the documentation (README.md, CHANGELOG.md, etc.) as necessary.
• I have run pre-commit and tox and all checks pass.
• This pull request is ready to be reviewed.