fix(relations): support models whose primary key is a OneToOneField

[d3vyce]

Description

Fixes three bugs with a model whose primary key is a OneToOneField. Both the relation and its <field>_id backing field are flagged pk, and these code paths took the relation, which has no column:

class User(Model):
    name = fields.CharField(50)

class Profile(Model):
    user = fields.OneToOneField("models.User", primary_key=True, related_name="profile")
    bio = fields.TextField()

class Post(Model):
    profile = fields.ForeignKeyField("models.Profile", related_name="posts")

# before: the "post" table has no "profile_id" column, the link is never written or read back
await Profile.get(pk=1)                          # FieldError: Unknown filter param 'pk'
await Profile.filter(user__name="ada").delete()  # KeyError: 'user' (same for update())

A ForeignKeyField to such a model now targets the backing field. Relations are set up in model name order, so when Post comes first, Profile.user is now initialized first, with or without to_field="user_id". That is also what makemigrations now writes: it wrote to_field='user', and the migrated table had no column either. Table names are now assigned before any relation, as Profile.user names its reverse relation after its table.

add_field() registers the pk filters for the backing field, which _init_relations adds after the class is created, and _pk_in_subquery() (#2269) only selects the pk fields that have a column.

Motivation and Context

I found no issue for these; related to #1771 / #1783 (many-to-many on such a model). A one-to-one primary key extends a table row for row, and other tables reference the extension: their foreign key silently stored nothing.

How Has This Been Tested?

New tests in tests/test_relations.py (foreign keys from models set up before and after the target, pk filters) and tests/test_queryset.py (delete and update through a related field), run on SQLite and PostgreSQL 18 (asyncpg). The full suite passes on SQLite and asyncpg. MySQL and MSSQL are left to CI.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

This fix has been partially implemented by Claude Opus 5.5. All modifications made by the AI have been reviewed by me.

[codspeed]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing d3vyce:fix/o2o-primary-key (39ac9e9) with develop (1f896c0)}