pmb: Make RunOutputTypeDefault and RunOutputTypePopen enums

This allows us to get rid of some of the validation in sanity_checks()
as mypy handles this validation at "build time", and any typos in the
enum instantiation would be a runtime error rather than a silent
failure.

Additionally, it allows us to encode some of the behaviour of the
different output types into the type definition itself by using methods.

Part-of: https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/merge_requests/2642
(cherry picked from commit 7d2f055bcb)

pmb: Fix PmbArgs containing a string for output

While the annotations were changed to suggest that the output property
of PmbArgs contains a RunOutputType, at runtime it actually contained a
string because the argument parsing code hadn't been adapted to create a
RunOutputType. Fix this, and also change it to RunOutputTypeDefault as
while at it as that's more accurate.

Fixes 7d2f055bcb
Part-of: https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/merge_requests/2644

pmb/chroot/initfs.py

@@ -6,7 +6,7 @@ import pmb.chroot.initfs_hooks
 import pmb.chroot.other
 import pmb.chroot.apk
 import pmb.config.pmaports
-from pmb.types import PmbArgs
+from pmb.types import PmbArgs, RunOutputTypeDefault
 import pmb.helpers.cli
 from pmb.core import Chroot
 from pmb.core.context import get_context
@@ -82,7 +82,7 @@ def ls(flavor: str | None, suffix: Chroot, extra: bool = False) -> None:
     if extra:
         tmp = "/tmp/initfs-extra-extracted"
     extract(flavor, suffix, extra)
-    pmb.chroot.root(["ls", "-lahR", "."], suffix, Path(tmp), "stdout")
+    pmb.chroot.root(["ls", "-lahR", "."], suffix, Path(tmp), RunOutputTypeDefault.STDOUT)
     pmb.chroot.root(["rm", "-r", tmp], suffix)