VMs now live in ONE place: chains/<name>/ owns the full implementation.
Previously split across node/vms/<name>/ (impl) + chains/<name>/main.go
(plugin wrapper). Now consolidated.
New layout:
chains/<name>vm/*.go — package <name>vm (VM code)
chains/<name>vm/cmd/plugin/main.go — package main (plugin binary)
chains/<name>vm/go.mod — module github.com/luxfi/chains/<name>vm
Moved 11 VMs: aivm, bridgevm, dexvm, graphvm, identityvm, keyvm,
oraclevm, quantumvm, relayvm, thresholdvm, zkvm.
External callers now import github.com/luxfi/chains/<name> directly.
