Fix slots usage and use more slots

[carsonip]

Use empty slots for ABC classes, otherwise classes which inherit from them will still have __dict__. Also use __slots__ for more classes.

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This change is 

[carsonip]

This saves ~200 bytes per object, because the object does not contain a __dict__, and there are also a marginal performance gain:

python benchmarks/record_batch_read.py

before:

.....................
batch_read_v0: Mean +- std dev: 1.23 ms +- 0.06 ms
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batch_read_v1: Mean +- std dev: 1.28 ms +- 0.10 ms
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batch_read_v2: Mean +- std dev: 961 us +- 82 us

after:

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batch_read_v0: Mean +- std dev: 1.18 ms +- 0.05 ms
.....................
batch_read_v1: Mean +- std dev: 1.20 ms +- 0.06 ms
.....................
batch_read_v2: Mean +- std dev: 950 us +- 55 us

[jeffwidman]

Thx!