The codec now holds wide EntityType variants boxed (MText, Helix,
Dimension, Hatch, Viewport, MultiLeader, Surface, Table, Ole2Frame,
Light, Extended). Constructors box their entity; nested patterns reach
a dimension through entities::dimension::as_dimension(_mut). Also
follows BlockAction::action_ids, LineTypeComplexData::source_flags and
the decimal tab stop with an explicit character.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Moves the flatten projection fns and command helpers into modules/draw/modify/flatten.rs (behavior unchanged) and adds flatten_plan / flatten_scene_apply to the COMMANDS suite.
Shares the benchmark harness between both suites, extracts the plan/batch/apply helpers out of the EXPLODE command arm, and adds the command_benchmarks target.
