feat(stdlib): Tiled P6 — infinite/chunked maps, .world stitching, base64+zstd (#74)

- Infinite/chunked maps: <chunk x y width height> (TMX) and JSON chunks[]
  (default 16x16) decode and flatten into the dense layer array, sized to the
  chunk union; the map's 0/0 header dimensions fall back to the flattened bounds.
- .world stitching: Tiled.world / Tiled.world_count / Tiled.world_map read a
  .world (JSON, reusing Json.parse) and list its member maps at their offsets.
- base64+zstd: a self-contained pure-Ludic Zstandard decompressor
  (runtime/native/zstd.ludic, RFC 8878) — the design's "largest single item,
  explicitly last". Frame header + raw/RLE/compressed blocks; raw/RLE and
  direct-weight Huffman literals; the full FSE sequence path (predefined,
  transcribed exactly from zstd's hardcoded tables since they're not rebuildable
  from the default distributions; RLE; FSE-described) with repeat offsets and
  execution. Decodes the low-entropy GID streams a tilemap produces; a high-
  entropy FSE-compressed-Huffman-weights block fails cleanly with -1 rather than
  emitting wrong bytes (documented scope).

Proven by library/tiled_p6.ludic (12 assertions): TMX + TMJ chunk flattening,
.world offsets, and a real zstd-compressed tile layer decoding byte-exactly to
its CSV baseline. x test: 97 passed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

changes/tiled-maps.md

@@ -10,3 +10,4 @@ type: feat
 - **P3 animated tiles + tile objects (#71)** — a tileset `<animation>` advances deterministically as a pure function of the fixed 60/s engine frame clock (`Tiled.frame_gid`/`Tiled.animated`), so an animated GID resolves at draw to the current frame's GID with its flip flags preserved and reproduces frame-for-frame across runs; `Tiled.draw_anim` draws a map with animations advanced. Object-layer entries with a `gid` render the tile image (with their own flips), bottom-anchored, as placeable sprites.
 - **P4 objects, properties, templates, spawning (#72)** — all object shapes (rectangle / ellipse / point / polygon / polyline / text) and custom properties parse and are queryable (`Tiled.object`, `Tiled.object_shape`, `Tiled.prop`/`Tiled.prop_int`/`Tiled.prop_type`); class properties resolve their defaults against a project custom-type table (`Tiled.load_types` over `objecttypes.xml`); template instances inherit their `.tx`/`.tj` template's fields; and an object maps onto Ludic components on demand (`Tiled.spawn`/`Tiled.spawn_layer`, off by default, via the reflection ABI).
 - **P5 breadth (#73)** — image layers (parallax + repeat) and group layers (flattened, with recursive offset/opacity/tint/visible; `Tiled.layer_kind`/`Tiled.layer_offsetx`/`Tiled.layer_tint`); the isometric / staggered / hexagonal orientation coordinate transforms (`Tiled.cell_x`/`Tiled.cell_y`, driving the tile draw so cells land at the correct screen coords); and Wang-set GID resolution through the standard resolver (the terrain-corner authoring concept is editor-side and ignored).
+- **P6 scale (#74)** — infinite/chunked maps: `<chunk>` (TMX) and JSON `chunks[]` decode and flatten into the dense layer; `.world` stitching (`Tiled.world`/`Tiled.world_count`/`Tiled.world_map`) lists member maps at their offsets; and a self-contained pure-Ludic **zstd** decompressor (`z_zstd`, RFC 8878) for base64+zstd layers — frame + raw/RLE/compressed blocks, raw/RLE/direct-weight-Huffman literals, and the full FSE sequence path — decoding the low-entropy GID streams a tilemap produces (a high-entropy FSE-compressed-Huffman-weights block fails cleanly with -1 rather than emitting wrong bytes).