This reverts commit https://github.com/ruby/delegate/commit/fc2bd0498af0.

https://github.com/ruby/delegate/commit/7d5c1e0842

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>

Tempfile uses DelegateClass and Tempfile should be able to be used
by different ractors.

https://github.com/ruby/delegate/commit/cad194260b

https://github.com/ruby/delegate/commit/5ee4189537

It's for minitest. We don't need it with test-unit.

https://github.com/ruby/delegate/commit/447cd43973

https://github.com/ruby/delegate/commit/2a91436284

This commit prevents "method redefined" warnings when overriding methods
within a `DelegateClass` block, such as in the following example:

  ```ruby
  Base = Class.new do
    def foo
      "foo"
    end
  end

  Overridden = DelegateClass(Base) do
    def foo
      super + "!"
    end
  end
  ```

Fixes https://bugs.ruby-lang.org/issues/19047.

https://github.com/ruby/delegate/commit/214fae86de

Also, make DelegateClass.instance_method fallback to superclass.

Fixes [Bug #16982]

In 2.6, SimpleDelegator would always use the target `respond_to?`

In 2.7.0 it doesn't if the target does not inherit from Object.

This breaks compatibility for delegated objects that inherit
from BasicObject and redefine `respond_to?`.

`Delegator.delegating_block` should delegate keyword arguments
separately.  [ruby-core:96949]

This makes it possible to initialize_clone to correctly not freeze
internal state if the freeze: false keyword is passed to clone.

If clone is called with freeze: true or no keyword, do not pass
a second argument to initialize_clone to keep backwards
compatibility.

This makes it so that external libraries that override
initialize_clone but do not support the freeze keyword will fail
with ArgumentError if passing freeze: false to clone.  I think that
is better than the current behavior, which succeeds but results in
an unfrozen object with frozen internals.

Fix related issues in set and delegate in stdlib.

Fixes [Bug #14266]