Update all documentation to reflect that custom types work automatically
with the #[task] macro, requiring only Clone + Send + Sync + 'static.
Documentation updates:
- README: Add custom types to features, new Custom Types section
- CHANGELOG: Document custom type improvement in [Unreleased]
- src/lib.rs: Add custom types example to main API docs
- src/task.rs: Update Task trait docs to mention macro-generated extraction
- src/extract.rs: Clarify ExtractInput is now internal-only (for task_fn)
- dagx-macros: Update macro docs to emphasize automatic type handling
New example:
- examples/custom_types.rs: Simple 120-line example showing User type
flowing through DAG with fan-out pattern (one output → two consumers)
demonstrating Arc wrapping is automatic and transparent
This makes the custom type capability discoverable and prominent for users,
turning a previous limitation into a headline feature.
