feat(disasm): render the loong64 families x/arch names Unknown

x/arch's Plan 9 renderer decodes thirty-odd scalar loong64 operations
perfectly but prints them as "Unknown OP args", and names the
sign-extension pair EXT.W.B/EXT.W.H "?".  The supplementary naming
pass re-renders them with the toolchain's own spellings: the families
whose operand order x/arch already prints the Plan 9 way trade only
the mnemonic, and the pointer loads and stores, the acquire loads,
the release stores, PRELD and ALSL are rebuilt from the decoded
arguments with the toolchain's operand order and its raw displacement
reading.  ADDU16I.D, a macro helper the assembler never takes as
input, keeps the decoder's Unknown render.

The loong64 parity fixture grows from 73 to 385 rows, pinning every
unique four-byte corpus word the decoder accepts, and the LL/SC
displacement divergence in the encoder is documented for asm.

Assisted-by: GLM 5.3

disasm/disasm.go

@@ -69,7 +69,7 @@ func Decode(a arch.Arch, code []byte, addr uint64) (Instruction, error) {
 		if err != nil {
 			return Instruction{Addr: addr, Text: "???", Len: 4}, nil
 		}
-		return Instruction{Addr: addr, Text: loong64asm.GoSyntax(inst, addr, nil), Len: 4}, nil
+		return Instruction{Addr: addr, Text: nameLoong64(inst, loong64asm.GoSyntax(inst, addr, nil)), Len: 4}, nil
 
 	default: // amd64
 		inst, err := x86asm.Decode(code, 64)