[kyo-ui] use non-resolving a.test in iframe/img attribute tests

Problem: IframeTest "iframe src attribute" and HtmlRendererTest
"ImgSrc.Absolute renders full URL" embed a real resolvable external
domain (example.com) as a loaded subresource. withUI navigates via
Browser.goto with the default Settle.NetworkIdle barrier, which does not
return until the page load event fires, and the load event waits for the
iframe/img subresource. On a runner whose egress to example.com is
blocked or slow, that subresource connection hangs, so the settle
barrier times out with "settle timeout after NetworkIdle (load event
also never fired)" and the leaf fails. This surfaced on windows-JS while
the identical JS code passed on linux-JS.

Solution: point both subresources at the RFC 6761 reserved a.test TLD,
which never resolves, so the subresource fails DNS immediately, the load
event fires, and the settle barrier returns fast. The sibling leaf
"iframe reactive src updates" already uses a.test and passes on the same
runner. The tests only assert the rendered src attribute string, so the
domain is irrelevant to what they verify.

Author: fwbrasil

kyo-ui/shared/src/test/scala/kyo/HtmlRendererTest.scala

@@ -757,12 +757,12 @@ class HtmlRendererTest extends UITest:
     }
 
     "ImgSrc.Absolute renders full URL" in {
-        withUI(UI.div(UI.img(ImgSrc.Absolute(HttpUrl.parse("https://example.com/logo.png").getOrThrow), "logo").id("i"))) {
+        withUI(UI.div(UI.img(ImgSrc.Absolute(HttpUrl.parse("https://a.test/logo.png").getOrThrow), "logo").id("i"))) {
             Browser.assertAttributeSatisfies(
                 Selector.id("i"),
                 "src",
                 "ignore"
-            )(s => s.contains("example.com") && s.contains("logo.png")).unit
+            )(s => s.contains("a.test") && s.contains("logo.png")).unit
         }
     }
 

kyo-ui/shared/src/test/scala/kyo/IframeTest.scala

@@ -13,8 +13,8 @@ class IframeTest extends UITest:
     }
 
     "iframe src attribute" in {
-        withUI(UI.div(UI.iframe("https://example.com/page").id("f"))) {
-            Browser.assertAttributeSatisfies(Selector.id("f"), "src", "ignore")(_.contains("example.com/page")).unit
+        withUI(UI.div(UI.iframe("https://a.test/page").id("f"))) {
+            Browser.assertAttributeSatisfies(Selector.id("f"), "src", "ignore")(_.contains("a.test/page")).unit
         }
     }