FURB142 fix should parenthesize generator expressions

[dscorbett]

Summary

The fix for for-loop-set-mutations (FURB142) should parenthesize unparenthesized generator expressions to avoid changing the program’s behavior. Example:

$ cat >furb142.py <<'# EOF'
s = set()
for x in ("abc", "def"):
    s.add(c for c in x)
# EOF

$ python furb142.py; echo $?
0

$ ruff check --isolated furb142.py --select FURB142 --preview --fix
Found 1 error (1 fixed, 0 remaining).

$ python furb142.py 2>&1 | tail -n 3
    s.update(c for c in x for x in ("abc", "def"))
                        ^
NameError: name 'x' is not defined

Version

ruff 0.14.2 (83a3bc4 2025-10-23)

[sohamukute]

I'm going to fix #21098. The fix involves modifying the Edit::range_replacement in refurb.rs to wrap the generator expression in parentheses, and I'll add a regression test.