fix(camera): handle camera object replacement

[aefly]

Problem

SPF keeps the address of the game's camera object and only re-reads it when the camera type changes. When the game replaces the object without changing the type (e.g. switching trucks in the interior view), SPF kept writing to the old, freed object:

• Camera writes from plugins (seat position, rotation, FOV, roll) were silently lost.
• The roll SPF re-applies every frame could land in reused memory and crash the game (ACCESS_VIOLATION in spf-framework.dll).
• "Reset" in the Camera window restored the first truck's defaults, since defaults were stored once per session.

Changes

• GameCameraManager::Update() asks the game for the active camera's live object every frame. If it changed, the camera is re-activated on the new object (one Info log line).
• Activation goes through a single ActivateCamera(), which also refreshes the verified-camera cache so cameras reading it (Free camera) get the same object.
• Default state is tracked per game object: a camera activated on another object (another truck) stores its defaults again, whether the object was replaced live or through a switch to another camera type. New IGameCamera::ForgetDefaults().
• Eight cameras redeclared their own m_defaultsSaved, hiding the one in IGameCamera: HasSavedDefaults() always returned false and StoreDefaultState() ran every frame. The duplicates are removed.

Every camera's OnDeactivate() only clears its pointer, so deactivating a camera whose object is already freed is safe.

Testing

• Switching trucks in the interior view: the camera is re-activated on the new object, plugin writes apply, no crash.
• "Reset to Defaults" in the Camera window restores the current truck's defaults.

[TrackAndTruckDevs]

Thanks for finding this, merging!