BitSetRange API (#2449)

* WIP: Add BitSetRange

* BitSetRange: various code format changes

* Try to fix scala random versioning

* Initial impl of BitSet.toRange, along with some helper method in BitSet

* BitPatRange: visibility and name changes:

* BitSetRange: tests

* BitSetRange: remove Random.between

* Move BitSetRange to BitSet.fromRange. Remove BitSetRange and toBitSetRanges

* Rename max_known_length -> MaxKnownLength in BitPat

* Apply suggestions from code review

Co-authored-by: Jack Koenig <jack.koenig3@gmail.com>

* add api fromRange(start:  BigInt, length: BigInt)

Co-authored-by: Jiuyang Liu <liu@jiuyang.me>
Co-authored-by: Jack Koenig <jack.koenig3@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>