[ZhuchkaTriplesix]

Closes #1430

Changes

1. Prevent duplicate onChanged invocations:
   • Removed onChanged: widget.onChanged from inner Material and Shadcn TextFields to avoid firing twice per keystroke alongside _effectiveController listener.
2. Prevent false positive onChanged on cursor / selection changes:
   • Added _lastText tracking in _QueryaCodeEditorState. _onTextChanged compares currentText == _lastText and skips firing when only selection/cursor changed.
3. Enable default syntax highlighting:
   • When widget.controller == null and widget.enableHighlighting == true, initialize _internalController using SyntaxHighlightService.createHighlightController so SQL/JSON syntax highlighting works out of the box.
4. React to language and highlighting changes in didUpdateWidget:
   • Reconfigures _internalController when language or enableHighlighting changes, preserving current text and selection.
5. Unit tests:
   • Added widget tests in test/core/editor/querya_code_editor_test.dart validating:
     • exactly one onChanged call per typed character edit.
     • 0 onChanged calls on cursor clicks and selection changes.
     • creation of QueryaHighlightController by default when enableHighlighting is true.
     • creation of plain TextEditingController when enableHighlighting is false.
     • seamless update of highlight controller and preservation of text on language change.