🚀 Improve Windows Npcap SDK Detection in build.rs

🧠 Overview

This update refactors the emit_windows_packet_sdk_links logic to make Npcap SDK detection more robust, maintainable, and cross-architecture compatible.

⚡ Key Improvements

🔥 1. Smarter SDK Discovery

• Supports multiple detection strategies:
  • NPCAP_SDK_DIR environment variable (highest priority)
  • Workspace-relative paths (../npcap-sdk/Lib)
  • Common installation directories
  • ProgramFiles / ProgramFiles(x86) auto-detection
• Eliminates duplicate path checks using HashSet

⚙️ 2. Architecture-Aware Linking

• Automatically detects target architecture (x86, x86_64)
• Dynamically searches in appropriate subdirectories (x64, x86)
• Removes hardcoded assumptions

💎 3. Cleaner & Modular Code

• Extracted helper functions:
  • has_required_libs() → validates SDK presence
  • arch_subdir() → resolves architecture-specific paths
• Improved readability and maintainability

🧪 4. Better Build Diagnostics

• Clear cargo:warning messages when:
  • SDK is found
  • SDK is missing
• Easier debugging in CI/CD environments

🚀 5. Safer Platform Handling

• Uses cfg!(target_os = "windows") instead of runtime env checks
• Ensures logic only runs on Windows targets

📦 Behavior

• Links against:
  • Packet.lib
  • wpcap.lib
• Emits correct cargo:rustc-link-search automatically
• Gracefully warns if SDK is not found (non-breaking)

💡 Why This Matters

• Improves developer experience (zero-config in most cases)
• Reduces CI failures due to missing SDK paths
• Ensures compatibility across different Windows setups
• Makes the build script production-ready

🔧 Optional Follow-ups

• Add Linux/macOS libpcap auto-detection
• Cache detected SDK path for faster builds
• Add strict mode to fail build if SDK is required