Remove mention to torch from CliffordBackend + typing + hide protected attributes from Clifford.__repr__

[renatomello]

Per title.

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.51%. Comparing base (4815b7a) to head (8ece9e2).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1801      +/-   ##
==========================================
- Coverage   99.51%   99.51%   -0.01%     
==========================================
  Files          79       79              
  Lines       13274    13273       -1     
==========================================
- Hits        13210    13209       -1     
  Misses         64       64              

Flag	Coverage Δ
unittests	99.51% <100.00%> (-0.01%)	⬇️

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.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.