Monocrate refactor (#107)

* [wip] big refactor

* restore accidentally deleted files

* fix ci

* restore accidentally deleted files

* fix all-features build

* fix some clippy warnings

* clippy fix

* fix ci

* document stuff

* add missing import

* add back (de)serialization and sparse matrix ops

* add examples

* reorganize stuff

* fix bench build

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Co-authored-by: sarah <>