Apple build graph with query, build, run, and test commands

Apple projects can now be modeled as a typed build graph directly in once.toml. This release adds Apple target kinds including apple_library, apple_framework, apple_application, and apple_test_bundle, plus the supporting Starlark prelude that lowers those target kinds into Once’s Rust graph schemas. You can inspect the graph with once query targets, once query capabilities, and once query schema, and materialize outputs with once build and once run and once test commands. Built products are written under .once/out/<target>/.