Feature/reactive runtime resilient to duplicate module instances

[hexplus]

Description

Makes the reactive runtime resilient to duplicate module instances.

When a bundler loads the reactive-core module more than once on a page — which
routinely happens under dependency pre-bundling (Vite optimizeDeps / esbuild,
where the same internal chunk is served twice: once with an ?v=<hash> query
and once raw) — reactivity silently died. The two copies formed independent
reactive "worlds": a signal() write notified one copy's queue while a reactive
binding had tracked itself through the other's, so the binding stopped updating
with no error thrown. Raw ESM usage was never affected.

This PR fixes it with a first-copy-wins, share-the-functions registry: the
first-loaded copy publishes its implementations on a globalThis registry
(keyed by a versioned Symbol.for), and every later copy re-exports the first
copy's functions. Exactly one copy's code runs, so all copies funnel through a
single source of truth — and because the running code is byte-identical to the
single-instance build, there's no hot-path indirection and no perf change.
(An earlier attempt that shared the state regressed binding/effect creation by
~70%; sharing the functions avoids that entirely — confirmed by interleaved
cold + warm benchmarks.)

Also adds a one-time, dev-only warning when a duplicate runtime is detected,
explaining how to de-duplicate (optimizeDeps.exclude / resolve.dedupe);
stripped from production builds.

Changes: src/reactivity/track-core.ts (new — implementations + state),
src/reactivity/track.ts (rewritten — registry shim), src/reactivity/batch.ts
(same pattern), src/core/signals/derived.ts (uses isTrackingSuspended()),
new tests/duplicate-instance.test.ts. Version 3.3.0 → 3.3.1, CHANGELOG
entry, and docs-site version badges bumped (en/es/zh).

Related Issue

Closes #

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• I have read CONTRIBUTING.md
• My code builds without errors
• I have tested my changes
• I have updated documentation if needed