Use dbus instead of zbus for desktop notifications (#423)

zbus adds an entire async runtime to the binary and brings 90
dependencies (102 to 192).

The final release binary size is 8.2M (4.2M stripped) with zbus and 6.3M
(2.8M stripped) with dbus. Statically linked, 8.5M (4.4M stripped) with
zbus and 6.8M (3.1M stripped).

Since the dbus runtime dependency is fairly common (for example used by
the google-chrome package on Ubuntu) I suspect most users will already
have it installed, or at least will be able to easily install it.

Runtime dependencies before:

    linux-vdso.so.1
    libgcc_s.so.1
    libc.so.6
    /lib64/ld-linux-x86-64.so.2

After:

    linux-vdso.so.1
    libdbus-1.so.3
    libgcc_s.so.1
    libc.so.6
    /lib64/ld-linux-x86-64.so.2
    libsystemd.so.0
    liblzma.so.5
    libzstd.so.1
    liblz4.so.1
    libcap.so.2
    libgcrypt.so.20
    libgpg-error.so.0

.github/workflows/ci.yml

@@ -158,4 +158,4 @@ jobs:
         run: |
           RUST_BACKTRACE=1 \
             cargo build --release --verbose --target=x86_64-unknown-linux-musl \
-              --features=desktop-notifications
+              --features=desktop-notifications-static-linking