Improve RoPE partial shift case

[laggui]

Checklist

• Confirmed that cargo run-checks command has been executed.

Related Issues/PRs

Follow-up to #3275

Changes

Added a small improvement to only compute the additional values required when shifting. So if the start position is still within the buffer positions, the tail is shifted to the head (slice assign) and only the new values are computed + attributed (slice assigned).

Testing

Added unit tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.39%. Comparing base (0f84161) to head (029910a).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3290   +/-   ##
=======================================
  Coverage   82.38%   82.39%           
=======================================
  Files         987      987           
  Lines      125627   125691   +64     
=======================================
+ Hits       103496   103561   +65     
+ Misses      22131    22130    -1     

☔ 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.