Fix: TestForm crashes on render and Save button remains disabled for selected quizzes

[rahul810050]

Description

1. The pageAmount computed property accesses getDataSize.questions.general
   before Firestore data-size finishes loading, causing a render-time crash.

This results in a render-time crash when opening the Create/Edit Test dialog
on a fresh load.

2. The Save button validation incorrectly applies random-quiz constraints
   to the selected quiz type, keeping the button disabled even after selecting
   valid questions.

Both issues are caused by assumptions about state availability and
validation scope.