fix: quiet build warnings

[dancormier]

We have several warnings that create noise when building our library.

Warning examples

Less mixin deprecation warnings

DEPRECATED WARNING: Calling a mixin without parentheses is deprecated in /home/runner/work/Stacks/Stacks/packages/stacks-classic/lib/atomic/borders.less on line 47, column 14:
  <w> 47 .byw3 { .btw3; .bbw3; }

Performance warning

WARNING in asset size limit: The following asset(s) exceed the recommended size limit (244 KiB).
This can impact web performance.
Assets: 
  docs.css (510 KiB)
  docs.js (289 KiB)
  entry.stacks-editor.js (1.52 MiB)

This PR resolves the Less deprecation issues and quiets performance warnings.

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