feat: Panic when an attribute has a wrongly-formatted value, but only in debug builds to easily spot bugs

[marc2332]

Closes #454

[codecov]

Codecov Report

Attention: Patch coverage is 67.25490% with 167 lines in your changes missing coverage. Please review.

Project coverage is 73.69%. Comparing base (094d2d5) to head (acb814f).

Files	Patch %	Lines
crates/state/src/font_style.rs	24.74%	73 Missing ⚠️
crates/state/src/layout.rs	64.55%	28 Missing ⚠️
crates/state/src/style.rs	54.23%	27 Missing ⚠️
crates/state/src/cursor.rs	71.79%	11 Missing ⚠️
crates/state/src/accessibility.rs	66.66%	9 Missing ⚠️
crates/state/src/parsing.rs	73.33%	4 Missing ⚠️
crates/state/src/values/font.rs	20.00%	4 Missing ⚠️
crates/state/src/transform.rs	85.71%	3 Missing ⚠️
crates/state/src/values/color.rs	89.28%	3 Missing ⚠️
crates/state/src/layer.rs	89.47%	2 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #759      +/-   ##
==========================================
+ Coverage   73.57%   73.69%   +0.11%     
==========================================
  Files         199      199              
  Lines       20397    20427      +30     
==========================================
+ Hits        15008    15053      +45     
+ Misses       5389     5374      -15     

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