TryParse function

[piotrkowalczuk]

Add TryParse function that completes the parsing API gradation:

• Parse - returns (UUID, error), caller handles the error
• TryParse - returns NullUUID, no error, no panic
• MustParse - returns UUID, panics on failure

TryParse is useful when the caller wants to attempt parsing without dealing with explicit error handling or risking a panic. It returns a NullUUID with Valid set to true on success and false on failure.