Summary

make_strings_unique(str_list) assigns unique_strs = str_list (an alias,
not a copy) and then modifies unique_strs[i], which silently mutates
the original str_list the caller passed in. Any code that retains a
reference to the original list will observe unexpected changes.

Reproduction

from skbase.utils._iter import make_strings_unique
names = ["a", "a", "b"]
result = make_strings_unique(names)
print(names)   # ['a_1', 'a_2', 'b'] -- original was mutated!

Expected Behavior

The input should not be modified. Only the returned list should be unique.

Suggested Fix

Replace unique_strs = str_list with unique_strs = list(str_list).