Parse AdGuard #$# CSS injection as style/remove actions

[ryanbr]

Summary

AdGuard's #$# CSS-injection syntax (e.g. businesshemden.com#$#.mnd-cookie-modal { display: none !important; }) was rejected outright as UnsupportedSyntax. This routes it through the same brace-body parser added in #678 for the uBO/ABP ##selector { ... } form, producing a Style (or remove: → Remove) action.

businesshemden.com#$#.mnd-cookie-modal { display: none !important; }
  →  Style(".mnd-cookie-modal" => "display: none !important;")

Details

• The between_sharps.starts_with('$') branch now consumes the $ and sets a flag instead of erroring. The existing ? and leading-@ handlers then cover the extended #$?# and exception #@$# forms with no extra code.
• A post-parse guard rejects any #$# rule that produced no action. This is the key safety check: ABP snippet injection also uses #$# but has no { ... } body (e.g. example.com#$#abort-on-property-read alert), and must stay unsupported rather than being misparsed as a plain CSS selector.
• #%# / #@%# (AdGuard JS/scriptlet) remain unsupported — scope is limited to the CSS style/remove form.

Behavior change

Two existing assertions in tests/unit/lists.rs that expected #$# / #@$# to be UnsupportedSyntax are updated to expect successful parsing — this is the intended contract change.

Tests

cargo fmt --check clean; full lib suite passes under both default and css-validation features. Adds adguard_css_injection (style, multi-class selector, remove:, ABP-snippet rejection, generic rejection) and adguard_css_injection_extended (#$?#).

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Supersedes #685 (that PR was opened from a fork, which makes the Performance CI step fail when it tries to post its results comment with a read-only token — no actual regression; all benchmark ratios were ≤ 1.00).

[github-actions]

Rust Benchmark

Details

Benchmark suite	Current: 77587df	Previous: 5d182e5	Ratio
rule-match-browserlike/brave-list	2184625955 ns/iter (± 28173310)	2241363322 ns/iter (± 47317273)	0.97
rule-match-first-request/brave-list	1194826 ns/iter (± 15325)	1216052 ns/iter (± 6861)	0.98
blocker_new/brave-list	134582719 ns/iter (± 545998)	138839767 ns/iter (± 844690)	0.97
blocker_new/brave-list-deserialize	27992332 ns/iter (± 261528)	31752836 ns/iter (± 821884)	0.88
memory-usage-final/brave-list-initial	11355668 B/iter (± 0)	11355668 B/iter (± 0)	1
memory-usage-final/brave-list-1000-requests	2612449 B/iter (± 0)	2612449 B/iter (± 0)	1
memory-usage-max/brave-list-initial/max	63576475 B/iter (± 0)	63576475 B/iter (± 0)	1
memory-usage-alloc-count/brave-list-initial/alloc-count	859963 allocs/iter (± 0)	859963 allocs/iter (± 0)	1
memory-usage-alloc-count/brave-list-1000-requests/alloc-count	74018 allocs/iter (± 0)	74018 allocs/iter (± 0)	1
url_cosmetic_resources/brave-list	188858 ns/iter (± 652)	191870 ns/iter (± 955)	0.98
cosmetic-class-id-match/brave-list	3579896 ns/iter (± 966608)	3552152 ns/iter (± 986336)	1.01

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