emitEncodingAnnotation
Emit a tensor_encoding diagnostic comment when spec carries a non-null tensorEncoding (set via sk.ainet.lang.tensor.ops.withTensorEncoding).
The emitted line has the shape:
// tensor_encoding: role=<role> index=<i> name=<spec.name> encoding=<enc.name>MLIR tools ignore comments but text round-trips preserve them, so this is the cheapest way to keep SKaiNET's quantization metadata visible through the StableHLO emit boundary until a structured attribute or quant-dialect lowering lands. Emits nothing when the spec has no encoding — a null sk.ainet.lang.tensor.storage.TensorEncoding is the unknown / not-carried state, intentionally distinct from TensorEncoding.Dense.
Parameters
Logical slot the spec occupies for the node being emitted (e.g. "input" for function arguments, "result" for node outputs). Free-form so individual converters can use finer-grained tags if they call this helper directly.
Positional index of the spec within its role, e.g. the output port index for a multi-result node.