build: Remove installation of backends from 'test' extra

[matthewfeickert]

Description

To be able to take advantage of PR #2340 in CI it requires the ability to select a subset of dependencies to install as well (c.f. Issue #2372). To do this, this PR decouples the installation of the test dependendies in the 'test' extra from the backends that are installed in the 'all' extra and now requires 'all' to be explicitly given.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Remove the 'all' extra from the 'test' extra installs and add 'all' to 
  the 'develop' extra.
* Add the 'all' extra to all install commands that also install the 'test' extra.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6a347f4) 98.28% compared to head (2a9532c) 98.28%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2373   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files          69       69           
  Lines        4539     4539           
  Branches      803      803           
=======================================
  Hits         4461     4461           
  Misses         45       45           
  Partials       33       33           

Flag	Coverage Δ
contrib	97.86% <ø> (ø)
doctest	60.71% <ø> (ø)
unittests-3.10	96.29% <ø> (ø)
unittests-3.11	96.29% <ø> (ø)
unittests-3.8	96.32% <ø> (ø)
unittests-3.9	96.34% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[matthewfeickert]

Merging this given no feedback, but we can iterate on revisions if there are future requests for changes.