2.2.26

• Implement WebVTT REGION block parsing in the reader. Cues
  referencing a region now get proper origin/extent geometry computed
  via W3C TTML-WebVTT mapping formulas, enabling correct cross-format
  conversion (e.g., VTT with regions → DFXP produces correct
  tts:origin and tts:extent).
• Fix .x/.y typo in geometry.py fit_to_screen() — the Y-axis safety
  guard was checking X twice instead of both axes.
• Fix _remove_noop_off_on_italics typo in SCC
  specialized_collections.
• Add empty-collection guard in _remove_spaces_at_end_of_the_line.
• Replace magic numbers with named _InstructionNode constants.
• Remove dead _remove_styles() method from WebVTT reader.
• Remove redundant if-guard and unused class attributes in WebVTT
  writer.