Fix connect scanner host detection issue#12

[lokiee0]

• Fix host detection logic in connect scanner where hosts were incorrectly reported as down when ports were closed but host was responding
• Improve channel handling with buffered channels and proper port counting
• Add mutex protection for concurrent latency updates
• Better error classification for connection states:
  • Connection refused/reset -> PortClosed (host up, port closed)
  • Timeout/no route -> PortFiltered (host down or filtered)
  • Other errors -> PortUnknown (host likely down)
• Set latency on first port response to ensure host is detected as up
• Add comprehensive tests for host detection scenarios

This fixes the issue where 'furious -s connect github.com' would incorrectly report 'Host is down' when the host was actually up but ports were closed.

Fixes #12