✨ feat(lang): rewrite standalone .attr to self.attr at AST stage

[harehare]

Standalone attribute selectors like .lang or .depth previously returned NONE because eval_selector treats Selector::Attr(_) as non-matching. They now rewrite to attr(self, "attrName") at parse time, enabling both read and |= assignment forms.

#1627

[codspeed-hq]

Merging this PR will not alter performance

✅ 29 untouched benchmarks

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_{Comparing feat/standalone-attr-selector (26e3e16) with main (4758cd9)¹}

Footnotes

1. No successful run was found on main (c1fdb4c) during the generation of this report, so 4758cd9 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩