fix: Prevent list modification during iteration in BrowserPool

[vdusek]

Both _identify_inactive_browsers and _close_inactive_browsers methods were modifying their respective lists (_active_browsers and _inactive_browsers) while iterating over them. This is a classic bug that can cause items to be skipped or raise RuntimeError.

The fix iterates over a copy of the list (list(...)) while modifying the original, ensuring all items are properly processed.

Co-Authored-By: Claude Opus 4.5 [email protected]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.48%. Comparing base (64c246b) to head (797a23c).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1703      +/-   ##
==========================================
- Coverage   92.49%   92.48%   -0.01%     
==========================================
  Files         157      157              
  Lines       10489    10489              
==========================================
- Hits         9702     9701       -1     
- Misses        787      788       +1     

Flag	Coverage Δ
unit	92.48% <100.00%> (-0.01%)	⬇️

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[Pijukatel]

Would this ever cause any problem? I think it is no issue in the current implementation, but it could be a hidden bug if the implementation changes. Not sure if that is good enough justification for the change :-D

_identify_inactive_browsers is sync, so it will run through the iteration without anyone modifying its list.
_close_inactive_browsers is async, so it can yield in the middle of the iteration and the _identify_inactive_browsers can start changing the list. But the worst-case scenario is that it will miss some freshly added inactive_browsers, which does not matter at all, because it is a RecurringTask that runs periodically, so they will be closed in the next run anyway.

[vdusek]

The point is, when you remove an item from a list during iteration, the iterator's index doesn't adjust, and the next item will be skipped.

lst = [1, 2, 3, 4]
for x in lst:
    print(x)
    if x == 2:
        lst.remove(x)
print(lst)

$ python run.py 
1
2
4
[1, 3, 4]

See e.g. this https://stackoverflow.com/questions/1637807/modifying-list-while-iterating

So this is clearly a bug.