test: add regression tests for PR #1907 URL crash fix

Tests cover the StringIndexOutOfBoundsException in Url.getPart() that
occurred when readEnd() trimmed trailing characters (e.g. ':') from a
detected URL but urlMarker indices remained pointing past the trimmed
string's end.

- UrlMarkerTest: three cases testing PORT/QUERY index at or beyond
  string length (the boundary conditions fixed by minOf clamping and
  the startIndex >= length guard)
- UrlsDetectorTest: regression for "今北産業" (no crash, 0 URLs) and
  for a bare "example.com:" host
- UrlParserTest: end-to-end regression for "今北産業" and "example.com:"

https://claude.ai/code/session_013rJ9iYndYVJgpYK2VazxL2

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/richtext/UrlParserTest.kt

@@ -281,6 +281,30 @@ class UrlParserTest {
             Urls(withScheme = emptySet()),
         )
 
+    /**
+     * Regression test for PR #1907: parsing a note whose content is only the Japanese phrase
+     * "今北産業" (a common internet abbreviation) must not throw a StringIndexOutOfBoundsException
+     * from Url.getPart() and must produce no detected URLs.
+     */
+    @Test
+    fun testImakitaSangyo() =
+        test(
+            "今北産業",
+            Urls(),
+        )
+
+    /**
+     * Regression test for PR #1907: a URL that ends with ':' causes readEnd() to trim it,
+     * but the PORT marker index was already set to buffer.length (one past the trimmed URL).
+     * Accessing host/port must not throw StringIndexOutOfBoundsException.
+     */
+    @Test
+    fun testUrlEndingWithColon() =
+        test(
+            "example.com:",
+            Urls(),
+        )
+
     @Test
     fun testHour() =
         test(