fix main loop hang cli subcommmands

[bodoque-01]

Found a problem with some legacy CLI subcommands, the audio-file-to-recognized-song and fingerprint-to-recognized-song hang indefinitely, never exiting.
These subcommands created a new glib::MainContext but never set it as the thread default. The future scheduled via main_context.spawn_local() was never polled and this (I think) made the Shazam API request never execute and main_loop.run() blocked forever doing nothing.
And after fixing this, The async block had no main_loop.quit() call, so after printing the result the main loop would keep running.

Tested using cargo run -- audio-file-to-recognized-song python-version/tests/stupeflip.wav

[marin-m]

Thanks!

[bodoque-01]

Thank you instead for the merge!