Migrate @mongodb-js/zstd off the prebuild-install install script so it installs under npm 12, which blocks dependency install scripts by default.

The driver prefers Node's built-in zstd (NODE-7097) and uses this package only as the fallback, including in the v8 line. The package is not retired, and the fallback must keep working wherever a package manager skips install scripts.

Approach

Same model as kerberos (NODE-7679, the pilot): each prebuilt binary is published as its own package, @mongodb-js/zstd-<target>, with os/cpu/libc fields. @mongodb-js/zstd lists them as exact-version optional dependencies, so the package manager installs only the matching one and no install script runs. Targets are the same as today's prebuilds. Platforms without a prebuild build from source manually, and a local build takes precedence.

Acceptance Criteria

Implementation Requirements

• prebuild-install dependency and the install script removed, "gypfile": false.
• Loader tries the local build, then the platform package, and throws an error naming the platform.
• Release workflow publishes the platform packages first, then @mongodb-js/zstd, with provenance and signing covering every tarball, as in NODE-7679.
• The @mongodb-js/zstd-* package names exist on npm with publishing configured.

Testing Requirements

• Loader test covers every target.
• CI installs the packed packages into a fresh project with npm 12 and loads the addon without approving install scripts.

Documentation Requirements

• README: platform packages and building from source.

Follow Up Requirements

• N/A