Implement all and allSettled for parallel task execution

.context/plan.md

@@ -15,7 +15,7 @@ Goal: implement `hardtry` incrementally with behavior locked by
 - [x] Phase 7 - Builder API + root namespace exports
 - [x] Phase 8 - `dispose` with `AsyncDisposableStack`
 - [x] Phase 9 - `gen`
-- [ ] Phase 10 - `all` and `allSettled`
+- [x] Phase 10 - `all` and `allSettled`
 - [ ] Phase 11 - `flow` + `$exit`
 - [ ] Phase 12 - Hardening + release readiness
 

AGENTS.md

@@ -26,3 +26,8 @@ This project was built with [`pastry`](https://github.com/adelrodriguez/pastry)
 
 - Prefer type inference whenever possible.
 - Do not add explicit return types unless required by tooling, declaration emit, or a public API contract.
+
+## Implementation Approach
+
+- Prefer a WET-first approach while behavior is still evolving: duplicate simple logic when it keeps intent obvious and local.
+- Move to DRY only after patterns stabilize and the abstraction clearly improves readability, maintenance, or correctness.