2.1.0

Added

• Draw the tortoise yourself. Three additions that only make sense
  together, for renderers that have to put the tortoise somewhere a Canvas
  cannot reach — a SwiftUI overlay, a sprite in another engine, a 3-D model
  standing on a real table in an immersive space:
  • TortoiseSprite.hidden (TortoiseUI) — the canvas animates the drawing
    exactly as before and draws no cursor. It is a property of one view,
    unlike hideTortoise(), which records a command and so travels with the
    drawing into every renderer and every serialized stream. With it,
    ViewportMode.autoFit insets by nothing — there is no sprite to keep
    clear of the edge — so the drawing runs edge to edge and any margin is the
    caller's to add
  • TortoisePlayer.currentTortoiseState (TortoiseUI) — where the tortoise
    is right now, position and heading interpolated between commands, so a
    cursor of your own walks with the line instead of jumping a command at a
    time. nil until the player is attached to a canvas. It changes on every
    display frame, so read it from somewhere already running once per frame
    rather than observing it from a SwiftUI body
  • ViewportMode.transform(canvasSize:viewSize:drawingBounds:spriteHalfExtent:)
    and TortoiseSprite.halfExtent are now public — the mapping from tortoise
    coordinates onto the view, so a custom cursor lands exactly where the
    built-in sprite would have. Reimplementing that mapping is the failure
    worth avoiding: it agrees on the day it is written and drifts silently
    afterwards
• TortoiseState.interpolated(toward:progress:) (TortoiseCore) — the state
  part-way through a command. Only position and heading move; pen state,
  colors, visibility and speed come from the state being interpolated from,
  because those change at a command rather than across one. The heading takes
  the short way round (350° → 10° sweeps 20° forward), and progress is
  clamped to 0...1. This is now the single implementation of that blend:
  CanvasRenderer and TortoisePlayer.currentTortoiseState both go through
  it, so a custom cursor cannot drift a fraction of a command away from the
  built-in sprite

Changed

• No behavior changes. TortoiseSprite gains a case, so an exhaustive
  switch over it in your own code needs one more arm — the only source-level
  effect of this release

What's Changed

• レンダラが 🐢 を自分で描けるようにする by @temoki in #47

Full Changelog: 2.0.0...2.1.0