optimize small Getters

After some profiling, i came to the conclusion that current running logic is too complex, in order to support `bytesRead`, we have two `Decoder` type, the overhead of `runGetIncremental` is noticeable when the getter is small(around 100ns compare to cereal on my machine).

This gives binary a disadvantage in various benchmarks, since lots of benchmark just focus on a single combinator, the overhead of running it render this kind of benchmarks meaningless.

There're cases we do need running small getters, but i haven't really need `bytesRead` yet. So let's find a way to improve `bytesRead`, or remove it ?

首先检查 issue 中描述的两个 Decoder 类型和 runGetIncremental 路径，然后使用现有基准测试复现报告中的小 getter 开销。将 bytesRead 要求与不需要它的情况进行比较，并确定是否可以改进或移除该要求。在不丢失所需 bytesRead 行为的情况下减少小 getter 开销，即视为完成。

由索引模型根据 Issue 内容生成。