Improve CI verbosity and some perf improvements

commit a193b1cf:

meson.recipe: Use shell.new_call() to output to logfile
subprocess.check_call() outputs to stdout, and that doesn't get
redirected to the log file, which is unnecessarily verbose.

commit 159b12f7:

recipes: Use self.config.python_exe instead of sys.executable

commit b537c2a7:

cerbero: Use Path.glob() instead of `ls`
This is faster, especially on Windows, and also fixes these spammy
warnings:

Exception ignored when trying to write to the signal wakeup fd:
BlockingIOError: [Errno 11] Resource temporarily unavailable

commit aaa99911:

cerbero: Print where profiling will be outputted when enabled

commit c5e43552:

cerbero: Set os.environ instead of editing it in-place
This is massively faster. Speeds up recipe parsing from 8.2s to 5.6s
on Linux.

commit 52655cb7:

cerbero: Cache the return value of config.get_env
The values will always be the same, so cache them. This speeds up
recipe parsing from 5.6s to 5.0s.

commit 4df005be:

cerbero: Cache the output of shell.ls_files
Sometimes we call it on the same files multiple times. Speeds up
recipe parsing + packaging from 5.0s to 4.8s.