gpu: nova-core: apply the one "use" item per line policy to commands.rs

gpu: nova-core: apply the one "use" item per line policy to commands.rs

As per [1], we need one "use" item per line, in order to reduce merge
conflicts. Furthermore, we need a trailing ", //" in order to tell
rustfmt(1) to leave it alone.

This does that for commands.rs, which is the only file in nova-core that
has any remaining instances of the old style.

[1] https://docs.kernel.org/rust/coding-guidelines.html#imports

Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Link: https://patch.msgid.link/20260310021125.117855-7-jhubbard@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>