fix: restore iota blocks, asm --format flag and prose after the syntax pass

asm/arm64_assemble.go

@@ -413,7 +413,7 @@ func encodeARM64AddSubImm(mnem string, ops []*ast.Operand) ([]byte, error) {
 	if len(ops) != 2 && len(ops) != 3 {
 		return nil, fmt.Errorf("%s expects 2 or 3 operands, got %d", mnem, len(ops))
 	}
-	v := int32(immFromOperand(ops[0]))
+	v := immFromOperand(ops[0])
 	rd := arm64RegNum(operandRegName(ops[len(ops)-1]))
 	rn := rd
 	if len(ops) == 3 {
@@ -606,7 +606,7 @@ func encodeARM64LoadImm(rd int, v int64, mnem string) ([]byte, error) {
 	// - C_ABCON0 (0 < v ≤ 4095): bitmask first for positive values
 	// - Negative values: MOVN first, then bitmask
 	// - C_MOVCON (movcon-eligible, outside ABCON range): MOVZ/MOVN first
-	tryBitmaskFirst := (d > 0 && d <= 0xFFF)
+	tryBitmaskFirst := d > 0 && d <= 0xFFF
 
 	if tryBitmaskFirst {
 		// Small immediate: try bitmask first (Go uses ORR for values like $1, $256).