feat: notebook for locus breaker and susie finemapping benchmark (#717)

* feat: notebook for locus breaker and susie finemapping benchmark

* fix: won't pass tests with matplotlib imported

* feat: ukb_ppp_fm benchmark notebook

* fix: check for nulls as well as nans

* fix: removing matplotlib

* fix: update notebooks

* chore: re-run ukb ppp notebook

* chore: rerun notebook