[0.12.0] Enable features rusty-soundtouch and rusty-libopus

Practically, this should not add extra dependencies since soundtouch is bundled in, and libopus is already required by mpv.

EDIT: using rusty-soundtouch makes the MSRV 1.89, which shouldnt be a issue in arch to my knowledge (latest stable rust is 1.90 as of edit)

This targets termusic version 0.12.0, please dont merge before then.

Weirdly, makepkg reports the following:

==> WARNING: Library listed in 'depends' is not required by any files: libopus.so

but a ldd termusic-server | grep opus reports:

        libopus.so.0 => /usr/lib/libopus.so.0 (0x00007f7135200000)

Do i somehow need to include the .0 in the depends list?

(note that i did this testing against the 0.12.0 release, manually updating the pkgver; not included in this PR)