feat: install chunk and rpp nightlies and betas with mise

[oglassdev]

mise's built-in github: backend handles stable releases, but it can't follow a nightly or beta channel and only sees the newest 100 GitHub releases. This plugin reads chunkzero/mise-registry, so channels and every exact version keep resolving.

• Each channel is its own tool: chunkzero:chunk-nightly and chunkzero:chunk-beta list only that channel's releases (so latest with prerelease = true picks its newest), and get their own caches and installs; chunkzero:chunk lists every release for exact pins. mise.lock pins the resolved version.
• BackendInstall downloads the platform archive, checks its sha256 against the registry with the system's sha256sum/shasum/Get-FileHash (backend plugins have no built-in hashing), and extracts it with its bundled runtime files. Registry versions must match the release version scheme, and paths are quoted for each shell.
• BackendExecEnv puts the install directory on PATH.

Checks: test/e2e.sh installs the current chunk nightly as chunkzero:chunk-nightly from a local registry copy, runs chunk --version, and confirms a wrong checksum is rejected. I also checked that a registry version containing shell syntax is rejected, an install path containing an apostrophe works, and github:chunkzero/chunk installs and runs the same archive for stable releases.

🤖 Generated with Claude Code