optimize memory issues (#767)

* optimize memory issues

1. introduce jemalloc support, which can dump current memory usage
2. reduce the GlobalEvent broadcaster memory usage.
3. reduce tcp & udp tunnel memory usage

TODO: if peer conn tunnel hangs, the unbounded channel of peer rpc
may consume lots of memory, which should be improved.

* select a port from 15888+ when port is 0

easytier/Cargo.toml

@@ -205,6 +205,14 @@ hickory-resolver = "0.24.4"
 
 bounded_join_set = "0.3.0"
 
+jemallocator = { version = "0.5.4", optional = true }
+jemalloc-ctl = { version = "0.5.4", optional = true }
+jemalloc-sys = { version = "0.5.4", features = [
+    "stats",
+    "profiling",
+    "unprefixed_malloc_on_supported_platforms",
+], optional = true }
+
 [target.'cfg(any(target_os = "linux", target_os = "macos", target_os = "windows", target_os = "freebsd"))'.dependencies]
 machine-uid = "0.5.3"
 
@@ -280,3 +288,4 @@ websocket = [
 ]
 smoltcp = ["dep:smoltcp", "dep:parking_lot"]
 socks5 = ["dep:smoltcp"]
+jemalloc = ["dep:jemallocator", "dep:jemalloc-ctl", "dep:jemalloc-sys"]