Migrate from optional dependencies to dependency groups

[hbelmiro]

Summary

Replace [project.optional-dependencies] with [dependency-groups]
(PEP 735) for lint, test, and
dev in pyproject.toml.

Why

1. Semantic correctness – optional dependencies are for package
   consumers. Lint/test/dev deps are internal and should not appear as
   installable extras.

2. Cleaner package metadata – these groups won't leak into the
   published wheel.

3. No self-references – the fragile kfp-components[lint] pattern
   is replaced by native include-group composition.

4. uv best practice – uv
   recommends
   dependency groups for dev workflows.

5. Better defaults – uv sync includes the dev group
   automatically; contributors no longer need --extra dev.