feat(core): isolate proxies per Nexo instance

[drusco]

BREAKING CHANGE:
Proxies and their metadata are now scoped per Nexo instance.

• map.proxies and map.tracables now store nested Maps keyed by Nexo instance id.
• Proxy traps (apply, get, set, etc.) have been refactored to resolve the proxy and wrapper using the instance-specific symbol.
• Introduced resolveProxy() utility for consistent lookup and error handling across traps.
• Proxy handlers are now generated using createHandlers(nexo.id) to ensure traps operate within the correct context.
• ProxyWrapper now maintains a reference to its owning Nexo instance.

This change ensures that multiple Nexo instances can operate independently on the same targets without cross-contamination of proxy state or behavior.

Developers upgrading to this version should verify that all traps are created through createHandlers() using the correct Nexo instance, and that global access patterns to proxy maps are updated to support the per-instance structure.

[github-actions]

🎉 This PR is included in version 2.0.0-next.1 🎉

The release is available on:

• npm package (@next dist-tag)
• GitHub release

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