migrate RadarUtils to swift

[ShiCheng-Lu]

a slow but swift migration

...

swift and objective-c is fully inter-op-able, the migration only requires converting the *.m file into a *.swift file.

If there are no other objective-c implementations that requires a swift class (i.e. all the references of a swift class are other swift classes), then the *.h file can be omitted, and the @objc tags can be removed, this is for internal interfaces only.

For public interfaces, the swift class can be marked public and then *.h header is not required if there are no more references in other headers.

shoutout to chatGPT for helping to convert the objective-C file into swift without too much pain.

something to note: UIApplication.shared.backgroundTimeRemaining when invalid returns 1.79769e+308 in swift, inf in obj-c. This value is only used as part of logging.

I've also tested building this branch with waypoint, and it's working properly.