CVE-2026-85999: Soup Sieve: Polynomial-time ReDoS (O(n²)) in the whitespace/comment trimming regex `RE_WS_END` (triggers on VALID selectors)

Before tokenizing, selector_iter trims leading/trailing whitespace and comments by running two regexes over the whole raw selector with .search(). The trailing one, RE_WS_END = re.compile(r'{WSC}*$'), is anchored only at the end ($), not the start. Because .search() retries the pattern at every offset, a long run of whitespace or CSS comments that is not sitting exactly at the end of the string makes each retry greedily consume the run and then fail $, producing O(n²) time. This triggers on perfectly valid selectors — e.g. a descendant combinator with a long whitespace gap, a + " "*n + b — so no malformed input is required. A single valid ~20 KB selector stalls the interpreter for ~10 s of CPU.