fix: pack weapons not showing on fighter cards (#1541)

## Summary

- Fix pack weapon profiles being excluded from fighter card display by
using `all_content()` in the `weapon_profiles_field` prefetch
- Fix form validation rejecting pack weapon profiles and upgrades when
adding equipment, by setting `with_packs()` querysets on
`weapon_profiles_field` and `upgrades_field`

## Test plan

- [x] Add a pack weapon with a named profile to a fighter via trading
post — assignment should be created
- [x] Verify the weapon and its profiles appear on the fighter card
- [x] Verify core (non-pack) weapons still work as before

Fixes #1540

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Author: tgvashworth

gyrinx/core/models/list.py

@@ -1478,7 +1478,10 @@ def with_related_data(self):
                     "listfighterequipmentassignment_set__content_equipment__contentweaponprofile_set",
                     queryset=ContentWeaponProfile.objects.all_content(),
                 ),
-                "listfighterequipmentassignment_set__weapon_profiles_field",
+                Prefetch(
+                    "listfighterequipmentassignment_set__weapon_profiles_field",
+                    queryset=ContentWeaponProfile.objects.all_content(),
+                ),
                 "listfighterequipmentassignment_set__weapon_accessories_field__modifiers",
                 "listfighterequipmentassignment_set__content_equipment__modifiers",
                 "listfighterequipmentassignment_set__upgrades_field__modifiers",