Add pundit-matchers gem and enhance indexed post handling

- Added `pundit-matchers` gem to improve policy testing capabilities.
- Updated `BlobsController` to support a new "tiny" size option for avatars.
- Enhanced `IndexablePostsHelper` with a `show_path` method for different postable types.
- Refactored `IndexedPost` model to include methods for retrieving artist information and external links.
- Modified `Domain::E621::Post` model to initialize `tags_array` as a hash.
- Updated views for indexed posts to support new display formats (gallery and table).
- Improved test coverage with new user factory and updated specs for controller and job behaviors.

test/fixtures/users.yml

@@ -1,11 +0,0 @@
-# Read about fixtures at https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
-
-# This model initially had no columns defined. If you add columns to the
-# model remove the "{}" from the fixture names and add the columns immediately
-# below each fixture, per the syntax in the comments below
-#
-one: {}
-# column: value
-#
-two: {}
-# column: value