Graceful asndb failure handling and report-phase cache fix

[liquidsec]

Summary

Closes #3215
Closes #3227

• ASN-as-targets (bbot -t ASN:15169): retries 3 times with a 3-second delay between attempts. If all retries fail, the scan aborts cleanly with a message directing the user to look up CIDR ranges manually and pass them directly with -t.
• Mid-scan ASN lookups (asn report module, waf_bypass): circuit breaker on ASNHelper trips after 5 consecutive failures, logs a single prominent warning, and returns UNKNOWN_ASN for all subsequent calls without hitting the network. The scan continues without ASN enrichment data.
• Cache key type normalization: asn_to_subnets() (used by ASN-as-target seed expansion) normalizes its input to int before calling asndb's lookup_asn(), matching asndb's int-keyed LRU cache so repeated lookups hit the cache instead of the network.
• Shared ASNHelper for seed expansion: ASN seed expansion routes through the shared, API-key-aware ASNHelper instead of a throwaway un-keyed ASNDB() client. generate_children() takes a required helpers argument.
• Report-phase network elimination: report() reads ASN metadata stored during handle_event() instead of re-fetching it from the API. Zero network calls at end of scan.
• Regression tests: report() makes no network requests; ASN-as-target retry/abort behavior; and seed expansion through the shared ASNHelper.

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 99.32432% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90%. Comparing base (ef65b09) to head (e310d5f).
⚠️ Report is 2 commits behind head on dev.

Files with missing lines	Patch %	Lines
bbot/core/event/helpers.py	86%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             dev   #3219    +/-   ##
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+ Coverage     90%     90%    +1%     
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  Files        453     453            
  Lines      46101   46203   +102     
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+ Hits       41211   41325   +114     
+ Misses      4890    4878    -12     

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