* initial impl of Bars, Staircase, Smooth modes

* fix fillTo for staircase and smooth paths

* fix pointSize

* [bars] adjust gap factor & reduce bar width to include stroke width. remove rounding to favor gap & width uniformity over edge crispness.

* remove line path fallback for too-dense data

* "Auto" points mode implies "Never" for Bars

* slightly reduce x axis tick density

* fix bars height calc, make bars crisp again.

* [bars] don't use hard-coded 'x' scale key

* refactor catmullRomFitting() to accept x & y coord arrays. restrict to processing only visible data range.

* move path building functions to own file

* export typed functions

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>