Make all header properties "quasi-lazy"?

[mhvk]

Make all header properties "quasi-lazy"?

[mhvk]

"Needs clarification" since we need to do more thorough performance checking to know whether this really is a bottle-neck and thus worthwile doing. There are also multiple options:

1. Just make all attributes lazy. This would involve making our own property decorator, and ensuring that if a header is changed, all cached values are deleted.
2. Even cache decoded header values (such as frame_nr). In principle the routines calculating those should be pretty fast, so caching may not help.

[mhvk]

Closing since we should just check performance and be informed by that.