Add regression test for FormattableNoticonRange UTF-16 shift

Tests that apply() returns the correct UTF-16 code unit count (12)
rather than grapheme cluster count (2) when the noticon value is a
multi-byte emoji like 👨‍👩‍👧‍👦.

Author: jkmassel

Tests/KeystoneTests/Tests/Features/Notifications/FormattableNotIconTests.swift

@@ -34,6 +34,35 @@ final class FormattableNotIconTests: XCTestCase {
         XCTAssertEqual(subject?.value, Constants.icon)
     }
 
+    // MARK: - apply(_:to:withShift:)
+
+    func testApplyReturnsUTF16ShiftForMultiByteNoticon() {
+        // 👨‍👩‍👧‍👦 is 1 grapheme cluster but 11 UTF-16 code units.
+        // The noticon string is value + " ", so 12 UTF-16 code units total.
+        // With the old .count code, the shift would have been 2 (1 emoji + 1 space).
+        let familyEmoji = "👨‍👩‍👧‍👦"
+        let noticonRange = FormattableNoticonRange(value: familyEmoji, range: NSRange(location: 0, length: 0))
+
+        let baseText = "Hello World"
+        let string = NSMutableAttributedString(string: baseText)
+
+        let styles = SnippetsContentStyles(rangeStylesMap: [
+            .noticon: [.foregroundColor: UIColor.red]
+        ])
+
+        let shift = noticonRange.apply(styles, to: string, withShift: 0)
+
+        // The noticon is familyEmoji + " " = 12 UTF-16 code units
+        let expectedShift = (familyEmoji + " ").utf16.count
+        XCTAssertEqual(shift, expectedShift, "Shift should equal the UTF-16 count of the noticon, not the grapheme cluster count")
+
+        // Verify styles were applied to the full noticon range
+        var effectiveRange = NSRange()
+        let color = string.attribute(.foregroundColor, at: 0, effectiveRange: &effectiveRange)
+        XCTAssertNotNil(color)
+        XCTAssertEqual(effectiveRange.length, expectedShift, "Style should cover the full UTF-16 range of the inserted noticon")
+    }
+
     private func mockProperties() -> NotificationContentRange.Properties {
         return NotificationContentRange.Properties(range: Constants.range)
     }