Add pyairtable.models.schema.FieldType enum

[mesozoic]

Fixes #437

[Copilot]

Pull Request Overview

This PR introduces a FieldType enum to provide type-safe field type constants for Airtable field types, replacing string literals throughout the codebase. The enum inherits from str to maintain backward compatibility with existing string-based code.

Key Changes

• Added FieldType string enum with all 33 supported Airtable field types
• Updated field configuration classes to use FieldType enum values in Literal type hints
• Migrated FIELD_TYPES_TO_CLASSES dictionary keys from string literals to enum values

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
pyairtable/models/schema.py	Defines the new FieldType enum and updates all field configuration type annotations to use it
pyairtable/orm/fields.py	Updates the FIELD_TYPES_TO_CLASSES dictionary to use FieldType enum keys instead of string literals
pyairtable/orm/generate.py	Replaces hardcoded field type strings with FieldType enum values in type checking logic
tests/test_models_schema.py	Adds comprehensive test coverage for the new FieldType enum

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[Copilot]

[nitpick] The custom __repr__ method is unnecessary. The default Enum.__repr__ already provides a suitable representation (e.g., <FieldType.SINGLE_LINE_TEXT: 'singleLineText'>). Unless there's a specific requirement for this exact format, the default should be sufficient.

Suggested change

	def __repr__(self) -> str:
	return f"FieldType({self.value!r})"

[mesozoic]

Nah, I think the existing representation is ugly, and I will have to stare at this all the time. 😁