Keep declarations after nested rules inside at-rules

[wahidrizka]

Outside at-rules, declarations after a nested rule keep their place (#92), but inside a bubbled at-rule they are all moved into one rule before the nested rules:

.a { @media (min-width: 1px) { color: red; & { color: blue } color: green } }

/* before: the element is blue */
@media (min-width: 1px) {.a { color: red; color: green } .a { color: blue } }

/* after, like Sass 1.105.1: the element is green */
@media (min-width: 1px) {.a { color: red } .a { color: blue }.a { color: green } }

atruleChilds() collected every declaration of the at-rule into one clone of the parent rule and prepended it. Now it starts a new clone after each nested rule and puts each one where its declarations were, like Rule() does outside at-rules. This covers @media, @supports, @layer, @container and @at-root (without: media). Declarations around a nested at-rule stay together, as in Sass, and unwrapped at-rules like @font-face do not change.

To check it, I compared main (9.0.0) and this branch with Sass on 4,000 distinct generated nested rules. 226 more now match Sass and none stopped matching; the 56 that had the same rules in another order are among them. Of the 293 that still differ, 56 changed: 54 are closer to Sass, and in the other 2 only the known :is(&) selectors differ. In Chrome 154, the output now gives the same color as native nesting for @media, @supports and a :where(.dark) & rule, where main differed in all three. The only changed output without a Sass reference is @at-root without a selector, which Sass rejects when it has declarations; it now keeps their order too.

The new test fails on main. bnt --coverage 100, oxlint and oxfmt --check pass.