fix: KCP/UDP resilience to ICMP resets; optional KCP congestion control

- treat ICMP-driven UDP socket errors (WSAECONNRESET 10054 on Windows,
  ECONNREFUSED on Linux) as packet loss in punch_udp and the KCP pump
  instead of tearing the session down; KCP retransmits through them and a
  truly dead link is still reaped by the pong/app-level timeouts
- resolve STUN hostnames via tokio::net::lookup_host so DNS never blocks a
  runtime worker; fix the inverted non-IPv4 error message
- add enable-kcp-congestion-control option (default on): switch the turbo
  profile to nc=0 so brief loss on constrained links no longer spirals into
  stalls; sender-side only, no wire negotiation
- pin kcp-sys to the rustdesk-patches branch: upstream main lost the
  RustDesk patches on the EasyTier sync, and this branch also wires
  set_kcp_config_factory into connection setup, making the option effective

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.lock

@@ -755,9 +755,9 @@ dependencies = [
 
 [[package]]
 name = "bindgen"
-version = "0.71.1"
+version = "0.72.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5f58bf3d7db68cfbac37cfc485a8d711e87e064c3d0fe0435b92f7a407f9d6b3"
+checksum = "993776b509cfb49c750f11b8f07a46fa23e0a1386ffc01fb1e7d343efc387895"
 dependencies = [
  "bitflags 2.9.1",
  "cexpr",
@@ -4276,11 +4276,11 @@ dependencies = [
 [[package]]
 name = "kcp-sys"
 version = "0.1.0"
-source = "git+https://github.com/rustdesk-org/kcp-sys#32a6c09fc6223f54aea83981a6aa8995931d29be"
+source = "git+https://github.com/rustdesk-org/kcp-sys?branch=rustdesk-patches#acd13bad5248c7ea0f4c0595a627c308af210fb1"
 dependencies = [
  "anyhow",
  "auto_impl",
- "bindgen 0.71.1",
+ "bindgen 0.72.1",
  "bitflags 2.9.1",
  "bytes",
  "cc",