add asset build system
- Build: A new parallel, incremental build system for Projects where Asset
subclasses define a build method that will produce the ingame representation
of that asset. It can output multiple artifacts, all of which will be combined
into a mapfs archive and patched onto the papermario-dx ROM.
- Project now owns the asset directories.
- AssetsArchive: mapfs archive reader/writer with linked list structure that
chains multiple archives together, enabling layered asset resolution where
project archives override base game archives.
- Projects can be built into ".diorama" files for distribution.
- PlayButton: One-click build-and-launch workflow that compiles engine ROM,
builds project assets, patches the ROM, and launches in ares.
- AssetsDir: Separates owned (project) vs read-only (engine) asset directories
- Revamped the CLI to be more cargo-like and added docs for it.