Add check_pydantic_core_version()

[samuelcolvin]

We should add a public method to pydantic that checks the correct version of pydantic_core is installed, and errors with a descriptive exception if not. The pydantic-core version should be hard coded, not use some metadata function.

This method should be public, but not be called by default - it exists to help those packaging pydantic and pydantic-core check they have compatible versions. Obviously we should call it during tests.

Related to pyodide/pyodide#5336.