fix: request Shizuku permissions only when necessary

[rushiiMachine]

Fixes #58

• Only request shizuku at startup if shizuku is the selected install method (not by default)
• Request and wait for shizuku perms again once installing and handle the event that permissions are denied/not available
• When switching install methods, check if shizuku is available and wait for permissions to be granted before confirming the change (previously this relied on shizuku was already granted at startup otherwise it disabled the switcher)

[rushiiMachine]

You should've probably shown a toast here otherwise it's changing a setting without telling the user.
Something like "Failed to obtain Shizuku permissions, reverting to PackageManager"