ref https://bugs.ruby-lang.org/issues/8846

Remaining are `limit`, `precision`, `scale`, and `type` (the symbol
version). These will remain on the column, since they mirror the options
to the `column` method in the schema definition DSL

- Add check for not deleting previously created fixtures, to overcome sti fixtures from multiple files
- Added fixtures and fixtures test to verify the same

- Fixed wrong fixtures duplicating data insertion in same table

 - Fixtures with non-string labels such as integers should be accessed
   using integer label as key. For eg. pirates(1) or pirates(42).
 - But this results in NotFound error because the label is converted into string before
   looking up into the fixtures hash.
 - After this commit, the label is converted into string only if its a
   symbol.
 - This issue was fount out while adding a test case for
   https://github.com/rails/rails/commit/7b910917.

Ruby 4.2 started doing `value.gsub('$LABEL', label)` for fixture label interpolation, but you can have have valid YAML where `label` isn't a String. 

For example:

```YAML
0:
  name: John
  email: johndoe@gmail.com
1:
  name: Jane
  email: janedoe@gmail.com
```

This YAML will create a label that is a Fixnum, causing `TypeError: no implicit conversion of Fixnum into String.`

For some reason changing `.find` to `.unscoped.find` in
https://github.com/rails/rails/commit/f766abd4cf3eb75469d3646cfb6d85e668c619f3
caused `scoping` to leak in some tests when run in isolation (looks like
a concurrency issue?). `relation_scoping_test.rb` is a case that failed.
From what I can tell it should not be possible, but changing to the
block form fixes it. There is a deeper issue that I can't seem to find.
/cc @senny

Prior to this patch you'd end up with an error like:

```
ActiveRecord::RecordNotFound: Couldn't find <Model> with 'id'=<id> [WHERE (<default_scope condition>)]
```

Hash#keys.each allocates an array of keys; Hash#each_key iterates through the
keys without allocating a new array. This is the reason why Hash#each_key
exists.

fix fixtures not loading if a belongs_to association is defined with a :foreign_key option that's a symbol

 - Added a note about some features which are not dependent on
   auto-generated ID's.
 - [ci skip]

These methods are not random so they should not belings to SecureRandom
module.

This partially reverts commit 1a203d5e.

Reason: It was committed by accident

Fix polymorphic to check for `options[:polymorphic]` instead of
`options.key? :polymorphic` and then reuse the method `polymorphic?`
method instead of constantly checking the same `options[:polymorphic]`.

Fix habtm reflection
Conflicts:
    activerecord/CHANGELOG.md
    activerecord/lib/active_record/counter_cache.rb
    activerecord/lib/active_record/reflection.rb
    activerecord/test/cases/reflection_test.rb

Allows fixtures to use their $LABEL as part of a string instead
of limiting use to the entire value.

    mark:
      first_name: $LABEL
      username: $LABEL1973
      email: $LABEL@$LABELmail.com

    users(:mark).first_name # => mark
    users(:mark).username   # => mark1973
    users(:mark).email      # => mark@markmail.com

This reverts commit 026d0555.

Conflicts:
	activerecord/lib/active_record/fixtures.rb

Fixes #13383

Fixes: #11524

Fixture files are passed through an ERB renderer before being read as
YAML. The rendering is currently done in the context of the main object,
so method definitons leak into other fixtures, and there is no clean
place to define fixture helpers.

After this commit, the ERB renderer will use a new subclass of
ActiveRecord::FixtureSet.context_class each time a fixture is rendered.