OTP constructor Null safety

1. otp
2. otp
3. OTP
4. OTP constructor

OTP class

1. Constructors
2. OTP
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Static properties
12. lastUsedCounter
13. lastUsedTime
14. useTOTPPaddingForHOTP
15. Static methods
16. constantTimeVerification
17. generateHOTPCode
18. generateHOTPCodeString
19. generateTOTPCode
20. generateTOTPCodeString
21. getAlgorithm
22. getInternalDigest
23. randomSecret
24. remainingSeconds