Add Support for multiple TypedExtra subclasses.

[devRaphe]

Handle Multiple @TypedExtras Annotations/Subclasses

Description

This PR enhances the flexibility of the Retrofit generator by allowing multiple TypedExtras subclass to be used on a single method. Previously, only one TypedExtras subclass was supported, limiting the ability to organise and group extra parameters. This change brings the behavior of TypedExtras subclass in line with how Extra subclasses are handled.

Changes

• Updated the logic of _getMapFromTypedExtras to include all @TypedExtras data
• Maintained backward compatibility with existing implementation

Implementation Details

• The _getMapFromTypedExtras method now iterates through all @TypedExtras annotations on a method, extracting and combining their field values.
• In case of conflicting keys across multiple @TypedExtras annotations, the later annotations take precedence.

Benefits

• Greater flexibility in organising and grouping extra parameters

Testing

• Added unit tests to verify the correct handling of multiple @TypedExtras annotations
• Ensured existing tests for @extra continue to pass
• Tested with various combinations of @extra, @TypedExtras, to ensure correct merging behaviour.

Example Usage

@TypedExtraSubclass1({'group1': 'value1'})
@TypedExtraSubclass2({'group2': 'value2'})
@GET('/endpoint')
Future<void> someMethod();

[devRaphe]

@trevorwang

[trevorwang]

Thanks for the contribution.