fix: support android shared tun fd groups

Android previously treated setTunFd as a single-instance update, and the
VpnService plugin could only expose one IPv4 address. That made shared
TUN members disable each other or leave only one address configured.

Group enabled Android TUN instances by shared dev_name, send the fd to
every compatible member, and only disable incompatible TUN users. Build
the Android VPN request from the whole running shared group and pass
every IPv4 address to VpnService.

The shared mobile dispatcher now owns current fd device state on a
process-level runtime. New setTunFd calls replace that state even when
the raw fd number is reused, and mobile TUN read/write/create failures
rebuild with backoff while preserving member registrations.

Protect shared member cleanup with per-registration ownership tokens, so
old async cleanup cannot unregister a recreated member or remove its
source claims. Mobile source addresses are registered in the dispatcher
without applying OS ifcfg changes, so Android-originated packets return
through the owning instance.

When one shared member stops while another remains, notify the frontend
to recalculate the VpnService config instead of leaving stale addresses
and routes. Serialize Android VpnService config recalculation so stale
async events cannot overwrite newer shared-group state.

If one shared member is not ready, rebuild from the healthy members and
retry the missing member later. If no healthy member remains, stop the
Android VPN service instead of keeping stale routes active.

tauri-plugin-vpnservice/src/models.rs

@@ -22,6 +22,7 @@ pub struct VoidRequest {}
 #[serde(rename_all = "camelCase")]
 pub struct StartVpnRequest {
     pub ipv4_addr: Option<String>,
+    pub ipv4_addrs: Option<Vec<String>>,
     pub routes: Option<Vec<String>>,
     pub dns: Option<String>,
     pub disallowed_applications: Option<Vec<String>>,
@@ -39,6 +40,7 @@ pub struct Status {
 pub struct VpnStatus {
     pub running: bool,
     pub ipv4_addr: Option<String>,
+    pub ipv4_addrs: Option<Vec<String>>,
     pub routes: Option<Vec<String>>,
     pub dns: Option<String>,
 }