Convert auth accessors to configuration object

[mamhoff]

What is this pull request for?

This converts the auth_accessors.rb module, which is purely configuration, to a configuration object.

All methods are still there, but deprecated, and a few accessors stay in lib/alchemy.rb as shortcuts.

Notable changes (remove if none)

We can now configure Alchemy's auth system entirely outside of a config.to_prepare block.

Checklist

• [x] I have followed Pull Request guidelines
• [x] I have added a detailed description into each commit message
• [x] I have added tests to cover this change

[codecov[bot]]

Codecov Report

:x: Patch coverage is 83.63636% with 18 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 96.93%. Comparing base (70677fc) to head (43681c3). :warning: Report is 121 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/alchemy/auth_accessors.rb	70.68%	17 Missing :warning:
lib/alchemy/errors.rb	66.66%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3418      +/-   ##
==========================================
- Coverage   97.13%   96.93%   -0.21%     
==========================================
  Files         279      281       +2     
  Lines        7374     7428      +54     
==========================================
+ Hits         7163     7200      +37     
- Misses        211      228      +17     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• :package: JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mamhoff]

Rebased on #3424 in order to get the raw_user_class reader.

[github-actions[bot]]

This pull request has not seen any activiy in a long time. Probably because of missing tests or a necessary rebase. This PR will be closed in 7 days if no further activity happens.