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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.19%. Comparing base (58218c7) to head (dc14497).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1139      +/-   ##
==========================================
+ Coverage   62.16%   62.19%   +0.03%     
==========================================
  Files          40       40              
  Lines        3898     3899       +1     
==========================================
+ Hits         2423     2425       +2     
+ Misses       1475     1474       -1     

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