Use ActiveRecord lazy loading

[AmShaegar13]

Currently, the gem is loaded right away and requires active_record. When this happens, the database configuration is required even to run basic tasks like assets:precompile on a build host, which is suboptimal. There are two possible ways to prevent that:

1. Set require: false for the active_snapshot gem in Gemfile and add an initializer that lazy loads it:

   gem 'active_snapshot', '~> 0.3.0', require: false

ActiveSupport.on_load(:active_record) do
  require 'active_snapshot'
end

However, this will make the user required for a snapshot. I don't know why exactly but it looks like this is a bug anyway. In Rails 7, belongs_to will always add a presence validation. When lazy loading the gem, this actually works so the user is not optional anymore.

2. Merge this pull request. It will mark the user optional and lazy load all the code. Therefor, I had to move the requirement of active_record' totest_helper.rb`.

[westonganger]

Yes :user should be optional. Lets do that separate from this PR and add a test for it.

[AmShaegar13]

Done.

[westonganger]

Were you planning to create a separate PR to add optional: true to :user association?

[westonganger]

Closing this as I've merged #36 which modifies this approach slightly.