lib.App: Make default env var names overridable

Add _default_*_env() helper methods that return the environment variable
names, and use them in __init__() instead of hard-coded strings. This
allows subclasses to override the names.

Signed-off-by: Jan Lindemann <jan@janware.com>

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

@@ -43,6 +43,18 @@ class App:  # export
             default = None,
         )
 
+    def _default_log_flags_env(self) -> str:
+        return 'JW_DEFAULT_LOG_FLAGS'
+
+    def _default_log_level_env(self) -> str:
+        return 'JW_DEFAULT_LOG_LEVEL'
+
+    def _default_log_file_env(self) -> str:
+        return 'JW_DEFAULT_LOG_FILE'
+
+    def _default_show_backtrace_env(self) -> str:
+        return 'JW_DEFAULT_SHOW_BACKTRACE'
+
     def __init__(
         self,
         description: str = '',
@@ -114,15 +126,15 @@ class App:  # export
         self.__args: Namespace | None = None
         self.__cmdline: str | None = None
         self.__default_log_flags: str = os.getenv(
-            'JW_DEFAULT_LOG_FLAGS', default = 'stderr,position,prio,color'
+            self._default_log_flags_env(), default = 'stderr,position,prio,color'
         )
         self.__default_log_level: str | int | None = os.getenv(
-            'JW_DEFAULT_LOG_LEVEL', default = NOTICE
+            self._default_log_level_env(), default = NOTICE
         )
         self.__default_log_file: str | None = os.getenv(
-            'JW_DEFAULT_LOG_FILE', default = None
+            self._default_log_file_env(), default = None
         )
-        backtrace: str | bool = os.getenv('JW_DEFAULT_SHOW_BACKTRACE', False)
+        backtrace: str | bool = os.getenv(self._default_show_backtrace_env(), False)
         self.__back_trace = isinstance(backtrace, str) and backtrace.lower() in {
             '1',
             'true',