switch to Pyside6

[2bndy5]

The main change that everything is centered around is moving to PySide6. This removes the dependency on ImageMagick to handle SVG files because PySide6 is much more consistent and reliable (and faster than using CLI). Additionally, using PySide6 also replaces the need for pillow as a image processing library.

Breaking changes

1. Jinja syntax is customized to be YAML friendly. Now also includes a yaml filter to represent complex color specs in layouts/templates.
2. Solid colors are validated using pydantic_extra_types
3. Colors from mkdocs-material (fetched from sphinx-immaterial html_theme_options) are only used during config loading. This means that any colors specified in layout and the social_cards config must be valid RGB/HSL strings or known color names
4. Re-prioritized rectangles to be rendered before ellipses
5. Polygon's points are clamped to layer size while also respecting any border specified
6. Renamed validators.base_model module to common.py as it houses all commonly used/referenced models in other validator modules.

Other changes

• revised layouts to be easily inherited for custom layouts (added a tutorial in the docs)
• adds support for color gradients (finally). Linear, Radial, and Conical types are supported. PySide6 comes with 180 presets to be used for gradient colors; these are now generated in a separate page. Preset gradients can also be modified using the custom colors field (which can also be used to create entirely new gradients)
• switch all pillow usage over to PySide6
• added math module to the jinja contexts
• leading and trailing whitespaces are removed because it looks wired to have leading spaces in centered text
• the border.width spec is now a positive float type thanks to the precision provided by PySide6.

[codecov-commenter]

Codecov Report

Merging #11 (c30673c) into main (c036986) will increase coverage by 1.28%. The diff coverage is 99.67%.

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
+ Coverage   98.14%   99.43%   +1.28%     
==========================================
  Files          14       14              
  Lines        1187     1418     +231     
==========================================
+ Hits         1165     1410     +245     
+ Misses         22        8      -14     

Files Changed	Coverage Δ
src/sphinx_social_cards/validators/layers.py	98.00% <92.59%> (-2.00%)	:arrow_down:
src/sphinx_social_cards/colors.py	100.00% <100.00%> (ø)
src/sphinx_social_cards/fonts.py	98.92% <100.00%> (+0.07%)	:arrow_up:
src/sphinx_social_cards/generator.py	100.00% <100.00%> (+0.33%)	:arrow_up:
src/sphinx_social_cards/images.py	99.14% <100.00%> (+10.59%)	:arrow_up:
src/sphinx_social_cards/validators/__init__.py	98.55% <100.00%> (+0.39%)	:arrow_up:
src/sphinx_social_cards/validators/common.py	100.00% <100.00%> (ø)
src/sphinx_social_cards/validators/contexts.py	100.00% <100.00%> (ø)
src/sphinx_social_cards/validators/layout.py	100.00% <100.00%> (ø)