Support branded dependency IDs

[XiNiHa]

Description

This PR updates Step.addDependency() to return a typed dependency ID instead of a plain number, which can then be used with methods like Step.getDep() and ExecutionValues.at() to retrieve the typed step/value.

Performance impact

These are type-level changes.

Security impact

No changes to runtime behavior.

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1bdc4f8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
grafast	Minor
postgraphile	Minor

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