Reduces the number of places that care about the internals of how we
store and type cast attributes. We do not need to go through the
dup/freeze dance, as you couldn't have saved a frozen new record anyway,
and that is the only time we would end up modifying the frozen hash.

Remove duplicated `@raw_attributes.keys`

Reduces the number of things outside of attribute methods that cares
about the details of how we store and type cast attributes

Specify a time zone when testing TZ aware attributes

Millisecond inequality causes failures on Travis

This is a follow up to #15556

@kuldeepaggarwal did submit this patch way back (#13624).

Add array support when time zone aware attributes are enabled

This is a regression test for 29844dd.

We cannot cache keys because arrays are mutable. We rather want to cache
the arrays. This behaviour is tailor-made for the usage pattern strongs
params is designed for.

In a forthcoming commit I am going to add a test that covers why we need
to cache by value.

Every strong params instance has a live span of a request, the cache goes
away with the object. Since strong params have such a concrete intention,
it would be interesting to see if there are actually any real-world use
cases that are an actual leak, one that practically may matter.

I am not convinced that the theoretical leak has any practical consequences,
but if it can be shown there are, then I believe we should either get rid of
the cache (which is an optimization), or else wipe it in the mutating API.

This reverts commit e63be276.

Fix capitalization

remove rubyforge.org that was shut down [ci skip]

/cc @tenderlove

Removed unused `klass` definitions from types

Only `Date` and `Time` are handled.

Remove composed_of special case from multi-parameter attributes

Don't mess with `_before_type_cast` for numeric types

As we move towards removing the `klass` method from `column`, the else
clause as it stands right now will become the only case.

This reverts commit be1db994, reversing
changes made to 6680ee94.

Reason: This changed a behavior where numeric attributes when receiving
blank values didn't change its value.

Don't mess with `_before_type_cast` for numeric types

Restore I18n.locale to default after test.

If i18n_with_controller_test.rb were to run first, the I18n.locale will
be changed to :de, and the following tests in base_test.rb will fail:

"subject gets default from I18n"
“default subject can have interpolations”
"translations are scoped properly"
"implicit multipart with default locale"

Restore test deliveries properly in ActionMailer.

`ActionMailer::Base.delivery_method` and
`ActionMailer::Base.perform_deliveries` have leaked states.

"delivery method can be customized per instance" and "delivery method
can be customized in subclasses not changing the parent" in
delivery_methods_test.rb will fail if test_helper_test.rb (in which
TestHelperMailerTest is inherited from ActionMailer::TestCase) runs
before it.

Add missing test cases for schema dumping defaults

[ci skip]

Before this patch, using `ActiveRecord::Base.primary_key_prefix_type`
with `:table_name_with_underscore` would change the `SchemaMigration` model
to have a primary key. This resulted in broken queries for PG because it tried
to return the inserted PK (which does not exist).

Closes #15051.
Closes #15419.

/cc @zuhao