✨ Implement unix:dir and unix:tmpdir for --address

According to https://dbus.freedesktop.org/doc/dbus-specification.html ,
for unix:tmpdir, the service _may_ create an abstract socket,
but is not required to do so, thus our implementation is the same as our
unix:dir, as suggested by the specification

src/bus/mod.rs

@@ -164,8 +164,16 @@ impl Bus {
 
                 addr
             }
-            UnixSocket::Dir(_) => bail!("`dir` transport is not supported (yet)."),
-            UnixSocket::TmpDir(_) => bail!("`tmpdir` transport is not supported (yet)."),
+            UnixSocket::Dir(dir) | UnixSocket::TmpDir(dir) => {
+                let path = dir.join(format!("dbus-{}", fastrand::u32(1_000_000..u32::MAX)));
+                let addr = SocketAddr::from_pathname(&path)?;
+                info!(
+                    "Listening on UNIX socket file `{}`.",
+                    path.to_string_lossy()
+                );
+
+                addr
+            }
             _ => bail!("Unsupported address."),
         };
         let std_listener =