TextShape: line_spacing, line_count, shadow and outline fields ignored

PBTextShape's `line_spacing`, `line_count`, `shadow_blur`, `shadow_offset_x/y`, `shadow_color`, `outline_width`, `outline_color` are deserialized but never read (`crates/scene_runner/src/update_world/text_shape.rs`; there's an old TODO comment on outline units at line 72).

Unity renders most of these (`SDKComponents/TextShape/TMPProSdkExtensions.cs`) with one quirk worth matching deliberately: their shadow underlay only activates when `shadow_offset_x|y != 0`, so blur/colour alone do nothing.