v4: Tie view registration to driver registration

[jtdub]

Description

Currently get_hconfig_view() in constructors.py uses a hardcoded isinstance chain to map drivers to views. Only 5 of 10 platforms have views; the rest raise ValueError. With #226 introducing driver registration, views should follow the same pattern.

Proposed Change

Add a view_class parameter to register_driver() or a separate register_view():

# Option A: view_class on register_driver
register_driver("MY_NOS", MyNOSDriver, view_class=MyNOSView)

# Option B: separate register_view
register_view(Platform.CISCO_IOS, HConfigViewCiscoIOS)

Built-in views are registered at import time alongside their drivers. get_hconfig_view() reads from the registry instead of using isinstance checks.

Benefits

• Users can provide views for custom platforms
• Users can override built-in views
• Eliminates the hardcoded isinstance chain in constructors.py
• get_hconfig_view() returns None (or raises a clear error) for platforms without views instead of a generic ValueError

Related

• v4: Driver registration system for user-defined and override drivers #226 (driver registration system)