resolves#102

This pull request introduces several improvements and bug fixes across the transforms, marks, and helpers in the codebase, focusing on more robust stacking, sorting, and recordizing logic. The most significant changes are enhancements to the stacking transforms with more comprehensive tests, improved sorting behavior for strings and dates, and better handling of raw value arrays in recordizing functions.

Transform logic improvements

• Refactored the stacking logic instack.ts to handle both grouped and unit stacking, ensuring series identities remain consistent and supporting more stacking modes. Added support for facet stacking and improved handling of raw value arrays.[1][2][3]
• Added extensive new tests forstackY andstackX transforms, covering basic, centered, normalized, facet, unit, and recordized array stacking scenarios.

Sorting enhancements

• Improved thesort transform to handle string and date sorting correctly usinglocaleCompare for strings and numeric comparison for dates. Also, non-finite sort values are mapped toInfinity to avoid sort errors.
• Updated sort tests to cover sorting by string and date channels, and refactored test data for broader coverage.[1][2][3]

Recordizing and accessor fixes

• ModifiedrecordizeX andrecordizeY to exclude irrelevant channels (x,x1,x2 ory,y1,y2) when the input data is a raw value array, preventing channel pollution and improving downstream transforms.[1][2]
• UpdatedresolveProp to use a more robust check for the presence ofRAW_VALUE on a datum, improving type safety.

Mark and formatting tweaks

• Changed number formatting inPlot.svelte andColorLegend.svelte for more compact and grouped number display, improving chart readability.[1][2]
• UpdatedAreaY.svelte to import required constants and functions for improved mark rendering.