Enable escaped curly brace test case and preserve empty CSS rules in output

[Copilot]

The #\{\}{background:lime;} rule was commented out in the escapes test with a note that the parser doesn't support it. The parser already handles this correctly via indexOfArrayWithBracketAndQuoteSupport which skips backslash-escaped characters when scanning for delimiters — so this was just a stale test exclusion.

Additionally, the compiler's rule() method was stripping CSS rules with empty declaration blocks (e.g. .\3A \({}, ##fake-id{}, #-a-b-c-{}`). These are valid CSS rules per the spec and should be preserved in the output.

• Uncommented #\{\}{background:lime;} in test/cases/escapes/input.css
• Fixed rule() in src/stringify/compiler.ts to preserve rules with empty declaration blocks instead of dropping them (outputs selector {} in formatted mode, selector{} in compressed mode)
• Updated golden files (ast.json, output.css, compressed.css) to include both the escaped curly brace rule and the previously-dropped empty-body rules

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[jogibear9988]

These rules here are still removed, but they are valid css!
Also the following ones....

[Copilot]

Fixed in f6d45e8. The compiler's rule() method was stripping rules with empty declaration blocks (!decls.length → return ''). Updated it to preserve these valid CSS rules. Empty rules now output as selector {} in formatted mode and selector{} in compressed mode. All 6 empty-body rules (.\\3A \\\({}, .\31 a2b3c{}, #\#fake-id{}, #\---{}, #-a-b-c-{}, #©{}`) are now preserved in the output.