refactor: clarify shared traits with associated entries

[ariesdevil]

Summary

• Replace ambiguous Raw* names in shared Theta/Tuple internals with semantic names.
• Make Entry an associated type of ThetaFamilySketchView.
• Simplify Union, Intersection, and A-not-B type constraints.
• Rename internal wrapper fields to state or operator.

Testing

• cargo test -p datasketches --features theta,tuple
• RUSTDOCFLAGS="-D warnings" cargo doc -p datasketches --no-deps --features theta,tuple

[tisonkun]

Generally LGTM. 3 comments here:

1. The following signature looks weird (not symmetrical). At least I need one more consideration.

        A: ThetaFamilySketchView,
        B: ThetaFamilySketchView<Entry = A::Entry>,

2. operator fields can be op?
3. I wonder if AnotB should be ANotB to follow camel case. See #155 (comment).

[ariesdevil]

Fixed, PTAL again.

[tisonkun]

Thanks for your contribution @ariesdevil!