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

[marc2332]

Closes https://github.com/marc2332/freya/issues/454

[codecov[bot]]

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

Additional details and impacted files

```diff @@ 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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