feat: adds circleci to oidc

[owlstronaut]

This pull request adds support for CircleCI as a provider of OpenID Connect (OIDC) tokens in CI environments, alongside existing support for GitHub Actions and GitLab. The implementation includes both code changes to detect and handle CircleCI OIDC tokens and new tests to ensure correct behavior.

Usage

In your .circleci/config.yml:

version: 2.1

jobs:
  publish:
    docker:
      - image: cimg/node:lts
    steps:
      - checkout
      - run:
          name: Publish to npm
          command: |
            NPM_AUDIENCE="npm:$(npm config get registry | sed 's|https\?://||;s|/$||')"
            NPM_ID_TOKEN=$(circleci run oidc get --claims "{\"aud\": \"$NPM_AUDIENCE\"}")
            npm publish

workflows:
  publish:
    jobs:
      - publish

Note: Unlike GitHub Actions and GitLab, CircleCI requires manually fetching the OIDC token with the correct audience claim using the circleci CLI.