fix(inbound, tun): Close proxy.Inbound in AlwaysOnInboundHandler and close Tun in tun.Handler

[Rynnya]

Fixes broken chain of Close() calls on TUN inbound.
On Windows this fixes dangling adapter after calling Close() on Instance, and, strangely, fixes timeout on first attempt to create adapter again after application reboot.
On Linux nothing technically changes (I'm not really sure if Tun.Start() is called by AlwaysOnInboundHandler)
On Darwin, Android and iOS nothing changes because they have empty Close() implementations.

[Fangliding]

#5464 (comment)

[Rynnya]

#5464 (comment)

Got tests on Linux, and while Tun.Start() wasn't called (because AlwaysOnInboundHandler.proxy of type proxy.Inbound doesn't implement common.Runnable), it didn't had any effect anyway (because tunnel, when opened, already in UP state)

Tun.Close(), however, did close tunnel device, just like it would if application would be closed instead; this doesn't affect processes where xray is used from the start and until application dies, but it does help with applications that would reuse tunnel after some downtime (less work with OS routing)