Add RoaringTreemap::contains_range and range_cardinality

[dchristle]

RoaringBitmap has contains_range and range_cardinality; RoaringTreemap does not.

Empty-range conventions match RoaringBitmap: contains_range returns true, range_cardinality returns 0.

New test file treemap_range_checks.rs mirrors range_checks.rs.

[Kerollmops]

Thank you very much for this PR. I see that Clippy may have been auto-updated and is triggering an error. Can you fix it quickly, please?

Overall, the PR looks good. I just have a small improvement proposal. Can you address it?

[Kerollmops]

The CI issue doesn't seems related to your code so I'll merge it. Thanks for the help!

[dchristle]

Thanks for the review and merge. Yes, the Clippy warning was on existing code this PR didn’t touch, so I think a newer Clippy version likely started flagging it.

FWIW I checked the for loop vs map(...).sum() with a local --release disassembly, and for this case they compiled equivalently on the tested target, so the difference looks stylistic rather than performance-driven. BTreeMap::range(...) already makes the loop iterator-driven, and the reduction is already obvious to the compiler.