Don't panic when matching pseudo-element selectors against unstyled elements

[nicoburns]

Summary

Fixes CRASHes in css/css-nesting/nesting-basic.html and css/css-nesting/contextually-invalid-selectors-003.html (2 → 0 crashes; both now PASS).

Nested rules under a pseudo-element rule (e.g. .test::before { & { ... } }) cause stylo to match a ::before selector component against regular elements during the initial style traversal. Blitz's TElement::match_pseudo_element called el.styles.primary() (which unwrap()s) on the candidate element, but during initial traversal an element's ElementData exists before its primary style has been computed, so this panicked with called Option::unwrap() on a None value at stylo data.rs:187.

Fix in match_pseudo_element:

- el.styles.primary().pseudo().or(...)
+ el.styles.get_primary().and_then(|s| s.pseudo()).or(...)

Treating "no primary style yet" as "no pseudo-element identity" is correct: only Blitz's synthesized pseudo-element/anonymous-box nodes carry a pseudo, and those always have styles by the time they are matched (the AnonymousBlock fallback is unaffected).

Not a stylo bug: the unwrap is in stylo convenience API; the root cause was Blitz assuming primary styles always exist during selector matching.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/a8bd4846bf354f33a6037fffaca1f583
Requested by: @nicoburns

WPT results

2 newly passing, 0 newly failing (net +2).

Full diff (2 changed tests)

+ Crash => Pass css/css-nesting/contextually-invalid-selectors-003.html
+ Crash => Pass css/css-nesting/nesting-basic.html

_{Generated by the WPT workflow.}

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