Add multi-module memory snapshots to wazero

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What this task asks for

Add coordinated capture, restore, diff, and serialization for multi-module memory snapshots. Capture, incrementally capture, and restore consistent memory snapshots across multiple WebAssembly modules. Expose reconstructed data, compressed data, versions, tags, and byte-level comparisons through the Snapshot interface. Validate module, baseline, module-count, and restore-size errors with the documented messages and error code. Assign gap-free coordinator versions and make coordinators and the named registry safe for concurrent use. Provide context helpers, summaries, snapshot chains, and portable marshal and unmarshal operations. Expose `NewSnapshotCoordinator()` from the experimental package.