On circular imports, use of forward references / model_rebuild in schemas

[zzstoatzz]

This is a place to discuss and form a plan to improve:

• issues with circular imports (we defer too much as a result of these issues)
• spread use of model_rebuild() it should only happen in prefect.main ideally

related issues / PRs:

• Dependency on import order in user-code #15957
• Performance: Add static TypeAdapters and reuse them.  #15047
• make re-usable TypeAdapter instances for client schemas #16089
• Circular Import in prefect.utilities.schema_tools #16434
• PydanticUserError when initializing client schema data models for flow run creation #18317

[aaazzam]

you want to build a ... DAG ... of dependencies?

[aaazzam]

Also #16434

[aaazzam]

Also #15957

[zzstoatzz]

👍 #15957 is the first one linked in the body - ill move #16434 in there too

[zzstoatzz]

#19344