chore: simplify implementation in Assets to one-liners

[skaldarnar]

There are only a few utility functions in Assets that use more than one line
of code. And even those can be simplified to fit into a single line by making
better use of the (functional) interfaces of Optional or by removing
unnecessary checks and early returns.

[keturn]

As these static functions rely on CoreRegistry, I think this entire class is slated for removal.

But in the meantime, this doesn't hurt.