type: fingerprint workflow job doesn't support NPM_TOKEN pre-processing for private registries (unlike type: build)

***Summary***
`type: build` in EAS Workflows has built-in NPM_TOKEN pre-processing that writes .npmrc auth before yarn install runs. type: fingerprint does not, making it unusable with private npm registries.

**Environment**
- EAS CLI: latest
- Package manager: Yarn 1.22.22 (Classic)
- Private registry: AWS CodeArtifact

**Current behavior**
When using type: fingerprint with env: { NPM_TOKEN: ... }:

EAS starts Yarn, which loads .npmrc into memory at startup
Our preinstall hook writes NPM_TOKEN to .npmrc on disk — but Yarn 1 already cached config
yarn install fails with 401 Unauthorized on the private registry
Fingerprint computation never completes

**Expected behavior**
type: fingerprint should write .npmrc auth before starting yarn install, the same way type: build does.

**Request**
Either:
Add NPM_TOKEN pre-processing to type: fingerprint (same as type: build), or
Allow steps: in type: fingerprint so we can write .npmrc before the sealed logic runs
This would unblock fingerprint-based build caching for any project using a private npm registry with Yarn 1.