API: Deprecate generic Counter<T extends Number> and replace with simpler Counter API

[nastra]

Most of the time using a non-generic Counter API with a long value is simpler, especially when it comes down to serializing/deserializing Counter results (since we'd need to know the underlying generic type as well).

Therefore we'd want to move away from Counter<T extends Number> and replace it with Counter.

[rdblue]

@nastra, I opened https://github.com/nastra/iceberg/pull/23 to remove the old counter implementations. Let me know what you think.

[rdblue]

I was able to remove IntCounter and LongCounter by moving Counter.NOOP definition into DefaultCounter. I think that's the main thing that we need to do to get this in.