ref: typehints, enum instead of raw string, abc and other (#1)

Full code coverage with annotations, fixing errors in various linters: ruff, wps, etc. Fixing errors in type checkers: ty, mypy, pyright. Formatting and bringing code to a consistent style, applying best practices in various aspects.

src/argenta/command/__init__.py

@@ -1,3 +1,12 @@
-__all__ = ["Command"]
+__all__ = [
+    "Command",
+    "PossibleValues",
+    "PredefinedFlags",
+    "InputCommand",
+    "Flags",
+    "Flag"
+]
 
-from argenta.command.models import Command
+from argenta.command.models import Command, InputCommand
+from argenta.command.flag import defaults as PredefinedFlags
+from argenta.command.flag import (Flag, Flags, PossibleValues)