related: rails/rails#51726

`_reflect_on_association` is also a private API and will may be broken, but it works
for both String and Symbol, absorbing type differences, so use this one.

related: rails/rails#51725

related: rails/rails#51725

By default, only `id` is output, so set `:all` to output all attributes for testing.
related: rails/rails#49765

ar-multitenant expects that #primary_key returns single column instead of composite primary_keys for backward compatibilities.

Previously overwriting #primary_key to return single pk, but since the timing for
writing @primary_key has changed since Rails 7.2, this way is no longer available.
Instead, overwriting `#reset_primary_key`, which handles calculating `@primary_key`.

related: citusdata#239 (comment)