Switch the current implementation to use btree_cursors

[ripytide]

The current implementation is very much a bodge of using the range method largely in a unintended fashion.

Instead I propose we switch to using btree_cursors, which is a new API that was proposed with the express intention of improving the implementations of interval collections such as this ones this project provides.

The btree_cursors feature is currently a nightly unstable feature so this would more concretely lock us onto the nightly version of rust than the currently used, but more work-a-roundable features we are using at the moment.

Overall I think this will greatly improve the simplicity of the code, and will also greatly improve the performance due to using more fit-for-purpose methods on the raw BTreeMap.

Related btree_cursors Issues and PRs
Tracking Issue: rust-lang/rust#107540
Proposal: rust-lang/libs-team#141
Implementation: rust-lang/rust#105641
Related Entry Proposal: rust-lang/libs-team#73

[ripytide]

I should probably report on my finished usage and experience after using the new feature on the tracking issue, if that's the right place for feedback I'm not sure.

[ripytide]

closing in favor of #25

[workingjubilee]

I should probably report on my finished usage and experience after using the new feature on the tracking issue, if that's the right place for feedback I'm not sure.

Probably.

[ripytide]

@workingjubilee I ended up not really using btree_cursors as much as I planned in favor of ripytide/btree_monstrousity . Hence I don't really have much feedback other than cursors seem useful it certain situations.