perf: optimize coupon list deserialization by pre-computing offset

[Fengzdadi]

Summary

Minor optimization to deserializeCouponList() in hll/coupon_list.go - pre-compute the offset instead of calculating listIntArrStart + it*4 in each iteration.

Related Issue

Closes #86

Changes

- for it := 0; it < couponCount; it++ {
-     list.couponIntArr[it] = int(binary.LittleEndian.Uint32(byteArray[listIntArrStart+it*4 : listIntArrStart+it*4+4]))
- }
+ base := listIntArrStart
+ for it := 0; it < couponCount; it++ {
+     list.couponIntArr[it] = int(binary.LittleEndian.Uint32(byteArray[base:]))
+     base += 4
+ }

Benchmark Results

Method	8 items	32 items	128 items	1024 items
Before	27.6 ns	75.4 ns	270 ns	2153 ns
After	26.8 ns	69.9 ns	253 ns	2000 ns

~7% improvement by replacing multiplication with addition per iteration.

Testing

All existing tests pass:

go test ./hll/