fix(nest-plugins-reference): register missing reference plugin entry …

Description

The pitch.

The reference package only exposed a handful of plugins as entry points (memory/lww_register, privacy/hybrid_x25519, datafacts/cid_facts, and the failure detectors). The remaining plugins were only reachable through the built-in fallback in nest-core, which is not the documented discovery path.

Add entry-point declarations for every plugin listed in the built-in fallback so that the PluginRegistry discovers them via the standard install-time mechanism documented in CONTRIBUTING.md.

Also add a regression test in nest-core that fails if a built-in plugin is not backed by an entry point, preventing the two registries from drifting out of sync again.