Replace the external `@pnpm/registry-mock` (Verdaccio) test dependency with an in-repo, in-process registry that serves package fixtures to **both** the pacquet Rust tests and the pnpm CLI (Jest) tests. No separately managed registry process is needed.
### How it works
- **Fixtures** live at `registry/.fixtures/packages/<name>/<version>/…`, moved verbatim from [`pnpm/registry-mock`](https://github.com/pnpm/registry-mock) (keyed by each `package.json`'s `name`+`version`).
- **`pnpm-registry-fixtures`** builds verdaccio-shaped storage from those fixtures; the in-tree **`pnpm-registry`** crate serves it.
- Files whose names differ only by case (`@pnpm.e2e/with-same-file-in-different-cases`) and `bundleDependencies` trees are composed **in memory** by the builder, since neither can be committed to the working tree.
- **pacquet**: `pacquet-testing-utils`' `TestRegistry` starts the server lazily (once per process) in proxy mode, serving `@pnpm.e2e` fixtures locally and falling through to the npm uplink for real packages (`is-positive`, `is-negative`, …) — matching how registry-mock behaved.
- **pnpm CLI**: the `with-registry` Jest `globalSetup` builds storage from the fixtures via the new `pnpm-registry-prepare` binary (built from source in the Test CI job) and serves it with `pnpm-registry`. `REGISTRY_MOCK_PORT` / `REGISTRY_MOCK_CREDENTIALS` / `getIntegrity` now come from `@pnpm/testing.registry-mock`.
### Result
`@pnpm/registry-mock` is removed from every manifest, the catalog, and `packageExtensions`; `cargo test` / `cargo nextest run` / `just test` and the pnpm CLI Jest suites all run registry-backed tests without launching Verdaccio.
Skips the minimumReleaseAge maturity check when the registry metadata
lacks the "time" field, instead of throwing ERR_PNPM_MISSING_TIME.
Defaults to true, and prints a warning once per affected package.
12 command test suites had near-identical ~50-field DEFAULT_OPTS objects
copy-pasted between them. Extract the common fields into a single shared
package so each suite only declares its overrides.
