3f-macro macro= memory-compiler binding

Bind a reg memory to a specific memory-compiler macro; the toolchain maps the inferred access ports onto the macro's pins instead of emitting a behavioral array. No code handles the attribute today.

Failing example (pyrope → expected Verilog instance)

// ram_macro.prp
mod ram_macro(we:bool, waddr:u10, raddr:u10, din:u32) -> (q:u32@[0]) {
  reg ram:[1024]u32:[macro="sram_32kx32"] = nil
  if we { ram[waddr] = din }
  q = ram[raddr]
}

// expected: the emitted netlist instantiates the macro instead of flops
module ram_macro(...);
  sram_32kx32 ram_i(/* ports mapped by the toolchain */);
endmodule

Docs (TBD markers)

• docs/pyrope/08-memories.md — RTL instantiation section, macro paragraph
• docs/pyrope/15-tbd.md

Done when

Compiling the example emits a sram_32kx32 instance (blackbox is fine; port-mapping rules need a small spec). Then drop the TBD note in 08-memories.