Implement auto route for tun inbound

[ibigbug]

Tenets

• clash-rs should handle traffic on given routes when tun inbound is enabled
• users should be able to tell the routes they want to proxy over tun
• should work on Windows/Linux/macOS
• we should try our best to resolve routes failures and give as much details when things don't work

Work Items

• smoltcp #228
• refactor(tun): use libtun #456
• feat(tun): fix tun mode on Windows #541
• feat(dns): bind interface on dns connections #552
• windows情况下tun模式无法使用 #396
• Have tun support multiple address #579
• platform
  • Windows
    • doesn't work - https://learn.microsoft.com/en-us/windows/win32/api/rtmv2/nf-rtmv2-rtmaddnexthop
    • use built in command instead
  • Linux - https://www.wireguard.com/netns/ either fwmark or ns
  • macOS - assumes route command is builtin
• ipv6 - blocked by Have tun support multiple address #579

Example config

tun:
  enable: true
  device-id: "dev://utun1989"
  routes:
    - 0.0.0.0/1
    - 128.0.0.0/1

Implementation

• Windows - feat(tun): windows auto-route #561
• macOS - feat(tun): auto route on macos #592
• Linux - feat(tun): route all on linux #594

[ibigbug]

@Itsusinn @VendettaReborn FYI. feel free to add/update