Replace the busted-based Lua test runner with a repo-local harness.
The new harness runs spec files directly under `nvim -ll`, ships its own
reporter and lightweight `luassert` shim, and keeps the helper/preload
flow used by the functional and unit test suites.
Keep the file boundary model shallow and busted-like by restoring `_G`,
`package.loaded`, `package.preload`, `arg`, and the process environment
between files, without carrying extra reset APIs or custom assertion
machinery.
Update the build and test entrypoints to use the new runner, add
black-box coverage for the harness itself, and drop the bundled
busted/luacheck dependency path.
AI-assisted: Codex
(cherry picked from commit 55f9c2136e)
NEW BUILD SYSTEM!
This is a MVP implementation which supports building the "nvim" binary,
including cross-compilation for some targets.
As an example, you can build a aarch64-macos binary from
an x86-64-linux-gnu host, or vice versa
Add CI target for build.zig currently for functionaltests on linux
x86_64 only
Follow up items:
- praxis for version and dependency bumping
- windows 💀
- full integration of libintl and gettext (or a desicion not to)
- update help and API metadata files
- installation into a $PREFIX
- more tests and linters
