Refactor build command to use BaseBuildCommand

Moved shared build logic from build.py to a new build_base.py, introducing BaseBuildCommand for common build functionality. Updated build.py to inherit from BaseBuildCommand instead of BaseFlutterCommand, and adjusted imports accordingly. This improves code organization and reuse for build-related CLI commands.

Author: FeodorFitsner

sdk/python/packages/flet-cli/src/flet_cli/commands/build.py

@@ -4,10 +4,10 @@
 from rich.live import Live
 from rich.progress import Progress
 
-from flet_cli.commands.flutter_base import BaseFlutterCommand, console
+from flet_cli.commands.build_base import BaseBuildCommand, console
 
 
-class Command(BaseFlutterCommand):
+class Command(BaseBuildCommand):
     """
     Build a Flet Python app into a platform-specific executable or
     installable bundle. It supports building for desktop (macOS, Linux, Windows), web,