Move to zbus for all dbus communications

[cooperlees]

• Move to async rust + zbus
• Generate new zbus traits into dbus module for respective systemd dbus buses
• Delete all dbus module usage + in Cargo.toml

This diff has not moved us to taking advantage of calling all dbus calls in parallel. Will do in dedicated diff if we decide to go forward here.

Pros:

• async
• More actively developed + liked zbus crate now used
• Drop libdbus dependency

Cons:

• 3.6MB vs. 1.4MB binary size
• More CPU used ... more than 3x "user" CPU time and 4x "sys" on same Fedora box reported using time

[zeenix]

3.6MB vs. 1.4MB binary size

This is known issue and I've some concrete plans/ideas on fixing this (help welcome!): https://github.com/dbus2/zbus/issues/304#issuecomment-2144780012

More CPU used ... more than 3x "user" CPU time and 4x "sys" on same Fedora box reported using time

Interesting. I'd not trust a simple time output comparison too much (you want to use something like criterion with cargo bench) but as I wrote on the Matrix channel, I recently removed the biggest performance bottleneck and the performance should now be a lot better. These changes aren't released yet but if you like to give it a try from our git main, that would be great.