HS: E37 tokenizer API (+17 tests)

Implements hs-tokens-of, hs-stream-token, hs-stream-consume,
hs-stream-has-more, hs-token-type, hs-token-value, hs-token-op?,
hs-raw->api-token, hs-eof-sentinel in runtime.sx.

Tokenizer emits whitespace tokens after the first content token;
stream functions skip them for look-ahead and consume. Parser
filters whitespace tokens at hs-parse entry. Dot/hash after close
brackets split into PERIOD/POUND + IDENTIFIER. Template escape \$
produces literal $.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/hyperscript/parser.sx

@@ -9,7 +9,9 @@
   (fn
     (tokens src)
     (let
-      ((p 0) (tok-len (len tokens)))
+      ((tokens (filter (fn (t) (not (= (get t "type") "whitespace"))) tokens))
+       (p 0)
+       (tok-len (len (filter (fn (t) (not (= (get t "type") "whitespace"))) tokens))))
       (define tp (fn () (if (< p tok-len) (nth tokens p) nil)))
       (define
         tp-type