Refactor @tko/lifecycle: composition over mixins, add Symbol.dispose

[brianmhunt]

Problem

@tko/lifecycle uses a mixin pattern (LifeCycle.mixInto()) that creates hidden dependencies and doesn't compose well. The mixin approach is an older pattern that makes the type system harder to reason about.

Proposal

1. Keep the disposal tracking — subscription tracking, anchorTo() cascading disposal, addDisposable() are all genuinely useful
2. Add Symbol.dispose / Symbol.asyncDispose — so TKO objects work with TC39 using declarations (ES2024+)
3. Deprecate LifeCycle.mixInto() — classes should extend or compose directly
4. Composition over inheritance — offer the disposal tracker as a composable utility, not a mixin

Scope

Touches multiple packages:

• @tko/lifecycle — the core change
• @tko/bind — BindingHandler extends LifeCycle
• @tko/utils.component — ComponentABC extends LifeCycle
• @tko/utils.jsx — JsxObserver extends LifeCycle
• @tko/binding.component — uses lifecycle methods
• @tko/builder — imports LifeCycle

Current usage of lifecycle methods across the codebase

• subscribe() — tracked observable subscriptions
• computed() — tracked computed creation
• addEventListener() — tracked DOM listeners with auto-cleanup
• anchorTo() — hierarchical parent-child disposal chains
• addDisposable() — accepts any object with dispose()
• dispose() — tears down all tracked resources