fix(asyncapi): promote nested pydantic to components/schemas

[legau]

Description

Promote nested Pydantic model definitions from message payloads (including oneOf cases) into components/schemas and replace inline schemas with $ref references. This resolves incorrect “inplace” embedding of nested models in generated AsyncAPI 3.0 documents.

Not sure if it is a good implementation, however tests are passing

Fixes #2443

Type of change

• Bug fix (a non-breaking change that resolves an issue)

Checklist

• My code adheres to the style guidelines of this project (just lint shows no errors)
• I have conducted a self-review of my own code
• I have made the necessary changes to the documentation
• My changes do not generate any new warnings
• I have added tests to validate the effectiveness of my fix or the functionality of my new feature
• Both new and existing unit tests pass successfully on my local environment by running just test-coverage
• I have ensured that static analysis tests are passing by running just static-analysis
• I have included code examples to illustrate the modifications

[CLAassistant]

All committers have signed the CLA.

[Lancetnik]

The current problem is not publisher-specific. As well it is not specific for 3.0.0 AsyncAPI version

It should exists for subscribers as well for (or with descriminator probably)

@subscibrer
async def handler(body: Model1 | Model2): ... 

So, can you please add tests and fix for 3.0.0 and 2.6.0 versions both? And place them somewhere near test_pydantic_model_mixed_regular. Alse, please add a link to the original Issue as a test docstring

[legau]

This should be good