Model.from_db() overrides without fetch_mode argument crash with TypeError on any query

[Adam Johnson]

The fetch modes feature added in Django 6.1 (#28586) made every query
iteration path pass a new fetch_mode keyword argument to
Model.from_db(). Any model that overrides from_db() with the
signature documented in the model instance reference —
from_db(cls, db, field_names, values), including the documented
_loaded_values example — now crashes on any database fetch:

TypeError: MyModel.from_db() got an unexpected keyword argument 'fetch_mode'

This worked on Django 6.0 and all earlier versions.

The proposed fix is to deprecate from_db() overrides that do not accept the new fetch_mode keyword argument, using django.utils.inspect to detect the override signature and conditionally pass fetch_mode or not, emitting a RemovedInDjango70Warning for old-signature overrides.