feat(asm): add opcode parameter support for macros
Grammar: opcode rule now accepts param_ref alternative, positional_arg
accepts OPCODE token. Lower pass defers ParamRef opcodes and wraps bare
OPCODE tokens in macro call arguments as strings. Expand pass resolves
opcode mnemonic strings to ALUOp/MemOp via MNEMONIC_TO_OP during
macro body cloning.
Enables: #reduce_2 op |> { &r <| ${op} } / #reduce_2 add