perf: Skip parseQuery when no QUERY parameters (W4)

validateParameters previously allocated a HashMap and ran
String.split on every request, even when the operation declared no
query parameters (the common case). Defer the parse to the first
QUERY parameter encountered; routes without query params now skip
the work entirely.

k6 throughput +3.3% (44.1k -> 45.5k rps), p95 -22 us.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thced

src/main/java/com/retailsvc/http/internal/RequestPreparationFilter.java

@@ -100,9 +100,12 @@ private String stripBasePath(String path) {
 
   private void validateParameters(
       HttpExchange exchange, Operation op, Map<String, String> pathParams) {
-    Map<String, String> query = parseQuery(exchange.getRequestURI().getQuery());
+    Map<String, String> query = null;
     for (Parameter p : op.parameters()) {
       String pointer = "/" + p.in().name().toLowerCase(Locale.ROOT) + "/" + p.name();
+      if (p.in() == Parameter.Location.QUERY && query == null) {
+        query = parseQuery(exchange.getRequestURI().getQuery());
+      }
       String value =
           switch (p.in()) {
             case PATH -> pathParams.get(p.name());