lib.Distro: Fix os-release and cascade macros

expand_macros() looks up each %{name} via getattr with '-' turned into '_',
but macro_names advertises two names that don't resolve: 'os-release' has
no corresponding attribute, and 'os-cascade' resolves to the list property
os_cascade, which str.replace() rejects. Both macros are listed in the
platform info help output, yet always fail when used in a format string.

The space-joined cascade string is the cascade property, and 'cascade' is
the macro name the make recipes and scripts already use, together with the
--format default in cmds/platform/CmdInfo.py.

Before the App.distro_* properties moved to Distro, the advertised macro
names were derived from the distro_* attribute names, so the advertised
macro was %{cascade}; the hand-written macro_names replaced it with the
list attribute's name.

- Add the missing os_release attribute as an alias of os_release_str
- Advertise the 'cascade' macro in macro_names instead of 'os-cascade',
  leaving os_cascade as the purely programmatic list
- Update the platform info help expected output accordingly
- Add unit tests for the os-release field parsers, the derived properties,
  and the expansion of every advertised macro

Signed-off-by: Jan Lindemann <jan@janware.com>
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.85.1

src/python/jw/pkg/lib/Distro.py

@@ -49,7 +49,7 @@ class Distro(abc.ABC):
         'name',
         'codename',
         'gnu-triplet',
-        'os-cascade',
+        'cascade',
         'os-release',
         'pkg-ext',
     ]
@@ -210,6 +210,12 @@ class Distro(abc.ABC):
             )
         return self.__os_release_str
 
+    # -- expand_macros() looks up macro names via getattr with '-' turned
+    # into '_', so 'os-release' needs this alias
+    @property
+    def os_release(self) -> str:
+        return self.os_release_str
+
     @cached_property
     def name(self) -> str:
         return self.os_release_field('NAME')
@@ -284,6 +290,8 @@ class Distro(abc.ABC):
 
     @classmethod
     def macros(cls) -> list[str]:
+        # -- The doubled percent is not a typo: the macros are embedded
+        # in an argparse help string, where %% escapes to a literal %
         return ['%%{' + name + '}' for name in cls.macro_names]
 
     def expand_macros(self, fmt: str | Iterable[str]) -> str | list[str]: