fix: don't count DNS errors against consecutive failure limit

[vringar]

Summary

• DNS resolution errors (dnsNotFound) are expected when crawling large domain lists and don't indicate browser/instrumentation failure
• Skip failure counter increment and browser restart for DNS errors, preventing premature crawl termination
• DNS errors are still properly recorded in crawl_history with status neterror

Closes #1116

Changes

• openwpm/browser_manager.py: Add is_dns_error check before incrementing failure_count and triggering browser restart

Test plan

• Run test/test_webdriver_utils.py::test_parse_neterror_integration to verify DNS errors are still recorded correctly
• Verify crawls with unreachable domains don't trigger browser restarts
• Run full test suite to check for regressions

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.74%. Comparing base (12fae22) to head (79ce7fe).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
openwpm/browser_manager.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1139      +/-   ##
==========================================
- Coverage   56.75%   56.74%   -0.02%     
==========================================
  Files          40       40              
  Lines        3908     3909       +1     
==========================================
  Hits         2218     2218              
- Misses       1690     1691       +1     

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