[BUG] Fix in-place mutation in make_strings_unique

[SHIVANSH-ux-ys]

Fixes #551

The function make_strings_unique was mutating the input list in-place due to a direct reference assignment. This PR ensures a copy is created before modification.

Verified with a reproduction script:

mylist = ["a", "b", "a"]
make_strings_unique(mylist)
# mylist remains ["a", "b", "a"]

[fkiraly]

Great, thanks!

Can you add a test against regression? I.e., testing that the function no longer mutates its input?

[SHIVANSH-ux-ys]

Hi @fkiraly,

I have added a regression test in skbase/utils/tests/test_iter.py to ensure that make_strings_unique does not mutate its input lists (verifying both flat and nested list inputs).

The test passes successfully. Ready for another review!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.14%. Comparing base (306958d) to head (c777ab0).
⚠️ Report is 209 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #553      +/-   ##
==========================================
- Coverage   85.07%   84.14%   -0.93%     
==========================================
  Files          45       52       +7     
  Lines        3015     3961     +946     
==========================================
+ Hits         2565     3333     +768     
- Misses        450      628     +178     

☔ 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.

[fkiraly]

Thanks!