Corepack does not work with COREPACK_NPM_REGISTRY that does not return signatures (Artifactory)

Related to https://github.com/nodejs/corepack/issues/537 and https://github.com/nodejs/corepack/issues/570

Corepack does not work with our registry as it does not return the field dist.signatures.
Here's a comparison of https://registry.npmjs.org/pnpm/10.12.4 and <our-artifactory-host>/artifactory/api/npm/default-npm-3rdparty/pnpm/10.12.4

npmjs:

"dist": {
    "shasum": "88a0ccfe72d6345dede50dc9d6158400be2420eb",
    "tarball": "https://registry.npmjs.org/pnpm/-/pnpm-10.12.4.tgz",
    "fileCount": 1111,
    "integrity": "sha512-Xqiw3u2U7WhpHJutTJVUknBcXuuKh++GvGLHSiawN7CP+VcPEIsuTb0d0akYb+qSXlJ/FBxkjoWvRWMQdGgBhA==",
    "signatures": [
      {
        "sig": "MEUCIHgFNYCynawsQj2TFih8MSo5NU8irHoWSjYIWoFdjXsUAiEArLjxP+kP0pDgYCk1HfGfrLjxph157UO/0WcQTCDmxTM=",
        "keyid": "SHA256:DhQ8wR5APBvFHLF/+Tc+AYvPOdTpcIDqOhxsBHRwC7U"
      }
    ],
    "unpackedSize": 17665923
  },

artifactory:

"dist" : {
    "tarball" : "<our-artifactory-host>/artifactory/api/npm/default-npm-3rdparty/pnpm/-/pnpm-10.12.4.tgz",
    "shasum" : "88a0ccfe72d6345dede50dc9d6158400be2420eb",
    "integrity" : "sha512-Xqiw3u2U7WhpHJutTJVUknBcXuuKh++GvGLHSiawN7CP+VcPEIsuTb0d0akYb+qSXlJ/FBxkjoWvRWMQdGgBhA=="
  },

Interestingly, <our-artifactory-host>/artifactory/api/npm/default-npm-3rdparty/pnpm/ returns the dist field just like npmjs, including signatures.

So maybe it is feasible to fetch the whole JSON for all versions as a fallback?

No file or test is named. Start by tracing how COREPACK_NPM_REGISTRY responses and the dist.signatures field are handled, then compare metadata from npmjs and Artifactory endpoints. Done means Corepack can handle the reported registry response without breaking signature verification or package-manager resolution.