`ActiveRecord::Base` does not (and has never) inherit from
`ActiveModel::Model`.

`ActiveModel::API` was introduced in as an extraction from
`ActiveModel::Model`. At that time (Sep 15, 2021), it was included back
into `ActiveModel::Model`, but was never included in `ActiveRecord` at
all.

The intent communicated around the introduction of `ActiveModel::API`
stated:

> By moving `ActiveModel::Model`'s implementation to a new
> `ActiveModel::API` we keep a definition of the minimum API to talk with
> Action Pack and Action View.

Active Record is also designed to integrate with Action Pack and Action
View. It already does (and its integration predates `ActiveModel::API`
by more than a decade). It's integration is powered by including and
extending the same set of foundational modules, with some
database-specific overrides.

This commit adds an `include ActiveModel::API` statement to
`ActiveRecord::Base`, then re-structures those overrides to comply with
the new module resolution order.

[c477d956]: https://github.com/rails/rails/commit/c477d95604e80e04d1aa8113a8236353235eb86a