fix(iOS): merge inline style with plain text (#722)

# Summary

This PR fixes merging inline style with plain text.
This regression was introduced in this PR:
#551

## Test Plan

1. run example app
2. toggle bold 
3. type `first line`
4. toggle off bold 
5. type `second`
6. go with the cursor before `second` and remove last bolded letter
7. bold style should not exceed on `second` word

## Screenshots / Videos
Before:


https://github.com/user-attachments/assets/92bc0425-9565-4acb-8ffe-359eab6aa9f0

After:


https://github.com/user-attachments/assets/38ea98fe-e497-4da2-9d31-6823702ff92b


## Compatibility

| OS      | Implemented |
| ------- | :---------: |
| iOS     |    ✅     |
| Android |    ❌     |
| Web     |    ❌     |

## Checklist

- [x] E2E tests are passing
- [x] Required E2E tests have been added (if applicable)

Author: kacperzolkiewski

.maestro/enrichedInput/flows/inline_styles_merge.yaml

@@ -0,0 +1,39 @@
+appId: swmansion.enriched.example
+---
+# Fix: merge inline styles with plain text
+- launchApp
+
+- tapOn:
+    id: 'toggle-screen-button'
+
+- tapOn:
+    id: 'editor-input'
+
+- tapOn:
+    id: 'toolbar-bold'
+- tapOn:
+    id: 'toolbar-italic'
+- tapOn:
+    id: 'toolbar-underline'
+
+- inputText: 'First line'
+- pressKey: Enter
+
+- tapOn:
+    id: 'toolbar-bold'
+- tapOn:
+    id: 'toolbar-italic'
+- tapOn:
+    id: 'toolbar-underline'
+- inputText: 'Second line'
+
+- tapOn:
+    id: 'editor-input'
+    point: '5%,75%'
+
+- pressKey: Backspace
+
+- runFlow:
+    file: '../subflows/capture_or_assert_screenshot.yaml'
+    env:
+      SCREENSHOT_NAME: 'inline_styles_merge'

.maestro/enrichedInput/screenshots/android/inline_styles_merge.png

@@ -1920,8 +1920,9 @@ - (bool)textView:(UITextView *)textView
             replacementText:(NSString *)text {
   // Capture the attributes at range.location that are being replaced
   // (autocorrect / predictive) so didProcessEditing: can re-stamp them onto the
-  // replacement.
-  if (range.length > 0) {
+  // replacement. Only capture for genuine replacements (text.length > 0), not
+  // for deletions/backspace (text.length == 0).
+  if (range.length > 0 && text.length > 0) {
     _capturedAttributesBeforeChange =
         [textView.textStorage attributesAtIndex:range.location
                                  effectiveRange:NULL];