fix(helpers): coerce Enum primary keys to .value in get_object_identifier

[AdarshJ173]

Summary

Fixes #955 — get_object_identifier() returns AnimalEnum.DOG instead of "dog" when the model primary key is an enum.Enum, breaking all edit/detail URLs for Enum-PK models.

Root cause

get_object_identifier() calls getattr(obj, pk.name) which returns the raw Enum instance as stored by SQLAlchemy (e.g. AnimalEnum.DOG). The single-PK fast-path returns this directly; the multi-PK path passes it through str(), which produces "AnimalEnum.DOG" rather than the underlying value "dog". Both paths therefore generate malformed admin URLs:

/admin/animal/edit/AnimalEnum.DOG   ← broken
/admin/animal/edit/dog              ← correct

What changed

sqladmin/helpers.py

Added a private _coerce_pk_value() helper that unwraps .value from any enum.Enum instance and is a no-op for all other types:

def _coerce_pk_value(value: Any) -> Any:
    if isinstance(value, enum.Enum):
        return value.value
    return value

get_object_identifier() now applies _coerce_pk_value() to each PK value before returning or joining:

- values = [getattr(obj, pk.name) for pk in primary_keys]
+ values = [_coerce_pk_value(getattr(obj, pk.name)) for pk in primary_keys]

• enum is already imported at the top of the module — no new imports.
• The helper is placed immediately before get_object_identifier() so it reads as a unit.
• No other call-sites are affected.

Acceptance criteria

• get_object_identifier(dog) returns "dog" (not AnimalEnum.DOG) for a str-Enum PK
• get_object_identifier(status) returns 1 (not StatusEnum.ACTIVE) for an int-Enum PK
• get_object_identifier(obj) continues to return the raw value for int, str, and UUID PKs (no regression)
• Multi-PK models with mixed Enum + non-Enum PKs serialise correctly

How to test

from enum import Enum
from sqladmin.helpers import get_object_identifier

class AnimalEnum(str, Enum):
    DOG = "dog"
    CAT = "cat"

class StatusEnum(int, Enum):
    ACTIVE = 1
    INACTIVE = 2

# Simulate a model instance with an Enum PK
class FakeAnimal:
    id = AnimalEnum.DOG

class FakeStatus:
    id = StatusEnum.ACTIVE

# Before this fix both assertions failed:
assert get_object_identifier(FakeAnimal()) == "dog"
assert get_object_identifier(FakeStatus()) == 1

(Full integration test: create an Animal SQLModel with id: AnimalEnum as PK, add it to an sqladmin view, open the admin list, click Edit — URL should be /admin/animal/edit/dog, not /admin/animal/edit/AnimalEnum.DOG.)

Notes

• No schema changes
• No new dependencies
• No server/API changes
• No breaking changes — _coerce_pk_value is a no-op for all non-Enum values; existing integer, string, and UUID primary keys are unaffected
• enum module was already imported at the top of helpers.py

[mmzeynalli]

This is duplicate of #1092, although this is better solution. If possible merge the tests of that PR to your PR (as you are missing tests). Do not copy, preferrably merge.