qualify path to Result type in the derive macro quotes

[iitalics]

Unqualified references to Result can cause problems when the user shadows the Result type in their own crate.

For example:

type Result<T> = std::result::Result<T, rustbus::connection::Error>;

#[derive(Debug, Clone, rustbus::Signature, rustbus::Unmarshal)]
struct SystemdUnitDescription {
    name: String,
    description: String,
    load_state: String,
    active_state: String,
    sub_state: String,
    followed: String,
    path: ObjectPath<String>,
    job_id: u32,
    job_type: String,
    job_path: ObjectPath<String>,
}

error[E0107]: type alias takes 1 generic argument but 2 generic arguments were supplied
  --> src/systemd.rs:97:44
   |
97 | #[derive(Debug, Clone, rustbus::Signature, rustbus::Unmarshal)]
   |                                            ^^^^^^^^^^^^^^^^^^
   |                                            |
   |                                            expected 1 generic argument
   |                                            help: remove this generic argument
   |
note: type alias defined here, with 1 generic parameter: `T`
  --> src/systemd.rs:95:6
   |
95 | type Result<T> = std::result::Result<T, rustbus::connection::Error>;
   |      ^^^^^^ -
   = note: this error originates in the derive macro `rustbus::Unmarshal` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0107`.
error: could not compile `dbus-experiments` (bin "dbus-experiments") due to previous error

[KillingSpark]

Oh damn, thanks! Macros sure have a lot of footguns.