…gistry tests

Modern package managers do not support unscoped authentication, and Yarn Classic's
metadata command (yarn info) does not propagate unscoped credentials correctly,
leading to 403 Forbidden failures on secure registries during ng update and ng add.

This commit removes the unscoped authentication test cases from both add and
update secure registry E2E tests, and cleans up the
createNpmConfigForAuthentication helper to default to scoped authentication.

Remove the non-standard forceAuth option and custom parsing for unscoped registry
credentials (token, username, password, auth) in package-metadata.ts.

Since the npm CLI does not support unscoped credentials and ignores them by
default, this aligning removes the unnecessary parsing complexity. Unscoped
credentials will now behave identically to any other standard configuration
property, falling through to default configuration parsing.

… using yarn

…ge manager

Bun's `pm view` command does not support requesting multiple fields at once (e.g. `pm view <pkg> dist-tags versions --json`), which is required by the default package manager abstraction to fetch package metadata during version compatibility search.

This change introduces a custom `getRegistryMetadata` handler in the package manager descriptor, allowing individual package managers to override registry metadata fetching entirely. The `bun` descriptor now implements this by querying `dist-tags` and `versions` separately in parallel, and returning the aggregated metadata object.