feat(strings): add MoveHashToEnd algorithm with tests

- Add MoveHashToEnd utility class that moves all '#' characters
  to the end of a string while preserving the order of other characters
- Algorithm runs in O(n) time and O(n) space using a two-pass approach:
  first collects non-'#' chars, then fills remaining positions with '#'
- Add null and empty string guards
- Add MoveHashToEndTest with 9 unit tests covering normal, edge,
  and boundary cases (null, empty, all-hash, no-hash, single char)

Author: ShyamChavda005

src/test/java/com/thealgorithms/strings/MoveHashToEndTest.java

@@ -0,0 +1,54 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+public class MoveHashToEndTest {
+
+    @Test
+    void testBasicCase() {
+        assertEquals("hello###", MoveHashToEnd.moveHashToEnd("h#e#l#llo"));
+    }
+
+    @Test
+    void testNoHash() {
+        assertEquals("hello", MoveHashToEnd.moveHashToEnd("hello"));
+    }
+
+    @Test
+    void testAllHashes() {
+        assertEquals("###", MoveHashToEnd.moveHashToEnd("###"));
+    }
+
+    @Test
+    void testHashAtEnd() {
+        assertEquals("hello#", MoveHashToEnd.moveHashToEnd("hello#"));
+    }
+
+    @Test
+    void testHashAtStart() {
+        assertEquals("hello#", MoveHashToEnd.moveHashToEnd("#hello"));
+    }
+
+    @Test
+    void testEmptyString() {
+        assertEquals("", MoveHashToEnd.moveHashToEnd(""));
+    }
+
+    @Test
+    void testNullInput() {
+        assertNull(MoveHashToEnd.moveHashToEnd(null));
+    }
+
+    @Test
+    void testSingleHash() {
+        assertEquals("#", MoveHashToEnd.moveHashToEnd("#"));
+    }
+
+    @Test
+    void testSingleNonHashChar() {
+        assertEquals("a", MoveHashToEnd.moveHashToEnd("a"));
+    }
+}