fix(slack): allow subject.id to be a number

[whitdog47]

This PR updates the Slack payload model to accept numeric subject IDs by enabling Pydantic’s coercion of numbers to strings.

[Copilot]

Pull Request Overview

This PR updates the Slack payload model to accept numeric subject IDs by enabling Pydantic’s coercion of numbers to strings.

• Imported ConfigDict from Pydantic.
• Added model_config on SubjectMetadata to coerce numeric IDs to strings.

Comments suppressed due to low confidence (2)

src/dispatch/plugins/dispatch_slack/models.py:41

• No tests were added to verify that numeric subject IDs are correctly coerced to strings. Consider adding unit tests that pass numeric ID values to this model and validate that they become strings.

coerce_numbers_to_str=True

src/dispatch/plugins/dispatch_slack/models.py:37

• The class docstring for SubjectMetadata doesn’t mention the new coercion behavior. Please update the docstring to explain that numeric IDs will be accepted and coerced to strings.

class SubjectMetadata(BaseModel):