Performance: DNS query batching and caching

Description

Implement DNS query batching and response caching to reduce DNS query latency and server load during discovery.

Current Behavior

• Sequential DNS queries (1 at a time)
• No caching of results
• Repeated queries for same domain
• High latency for bulk operations (SRV, A, MX queries)

Proposed Implementation

1. DNS Query Batching

   • Batch queries by type (A, AAAA, SRV, MX, PTR)
   • ThreadPoolExecutor with 32 workers for parallel queries
   • Concurrent resolution of multiple domains

2. Response Caching

   • In-memory cache (LRU, max 1000 entries)
   • TTL-aware expiration
   • Persistent optional cache (SQLite)
   • Cache invalidation on manual request

3. Query Optimization

   • Deduplicate identical queries
   • Batch reverse DNS lookups (PTR)
   • Parallel SRV record queries
   • Fallback chain optimization

Requirements

• 20-30x speedup on bulk DNS queries (100+ lookups)
• Memory usage < 50MB for cached data
• Configurable cache size and TTL
• Per-tool DNS query metrics

Files to Update

• adpentest/core.py - Integrate batching
• Update: GLOBAL_DNS_CONFIG class
• Add: DNS cache class

Success Criteria

• 100 domain queries: < 2 seconds (vs ~30s sequential)
• Cache hit rate > 70% on repeated queries
• No cache invalidation issues under race conditions