[TransferEngine]chore: replace slices vector with slice counter

[RuixiangMa]

Since the slices are solely utilized for counting purposes, replace them with counters to eliminate memory overhead

[alogfans]

LGTM

[stmatengss]

Why use slice counter to replace slices vector? It is a performance consideration or something?

[RuixiangMa]

Why use slice counter to replace slices vector? It is a performance consideration or something?

In the origin design, it appears that the sole requirement is for counting functionality.
Accessing and updating a single counter is generally faster than manipulating a vector, especially as the size of the vector grows. Operations like insertion on vectors can become costly as they may require shifting elements.