Allow configuration via environment variables

[youdie006]

🤔 What's changed?

Each configuration option can now be set via an environment variable (#2347). An option's key is converted to CUCUMBER_OPTION_<SCREAMING_SNAKE> — e.g. retryTagFilter → CUCUMBER_OPTION_RETRY_TAG_FILTER — following @davidjgoss's design in the issue.

• Precedence: CLI > environment > config file > default (env slots into mergeConfigurations between the config file and CLI), preserving the existing merge-vs-overwrite semantics (e.g. CUCUMBER_OPTION_TAGS and --tags combine into (@a) and (@b)).
• Values are parsed as JSON where possible (booleans / numbers / arrays) and validated against the config schema; unknown CUCUMBER_OPTION_* vars are ignored. Profile-level options are out of scope, per the issue.
• New internal fromEnv module; the public API surface is unchanged (verified by api-extractor).

⚡️ What's your motivation?

Fixes #2347 — lets every configuration option be provided via the environment (useful in CI), which previously wasn't possible for most options.

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

The precedence placement (env between config file and CLI) and the CUCUMBER_OPTION_TAGS merge semantics — happy to adjust if you'd prefer different behaviour. Quick manual check: CUCUMBER_OPTION_DRY_RUN=true skips scenarios; CUCUMBER_OPTION_TAGS='@wip' with --tags 'not @wip' resolves to (@wip) and (not @wip).

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[davidjgoss]

Thanks for raising this @youdie006. It looks good at a glance, but please can you follow the standard pull request template including the CoC acknowledgement:
https://raw.githubusercontent.com/cucumber/.github/refs/heads/main/.github/PULL_REQUEST_TEMPLATE.md

[youdie006]

Thanks @davidjgoss! I've updated the description to the standard template with the Code of Conduct acknowledgement, and pointed the CHANGELOG entry at this PR. Ready for another look when you have a moment.

[davidjgoss]

Thanks again. A couple of suggestions to improve.

[davidjgoss]

This is an implementation detail and we could do without having it in the user-facing documentation.

[davidjgoss]

Looking at this now, I think my steer to have CUCUMBER_OPTION be the prefix we look for was a mistake and it's led us to a more complex implementation than is needed.

First, there are no collisions with other env vars, and given we also support CUCUMBER_PUBLISH_URL and CUCUMBER_PUBLISH_TOKEN, having the extra prefix causes fragmentation from a user perspective. So I think just e.g. CUCUMBER_RETRY_TAG_FILTER is fine.

Second, we already have the list of option names to check (from the default flag config object), so we can have fewer loops and less code by simply iterating over those keys, and for each one forming the env var key and checking env for it - no need to iterate over the whole env object.