Further simplify the offset validation

[HaoYang670]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
This is the follow-up of #1684 (comment).

Describe the solution you'd like

How do we validate offsets now?

1. check if each offset can be converted to usize
2. check if each offset exceeds the offset_limit
3. check if offsets are monotonically increasing
4. validate each slot.

How could we simplify this process?

1. check if the last offset exceeds the offset_limit
2. check if each offset can be converted to usize (actually, this could also be removed. But we need to convert the type of offset to usize, so reserve it)
3. check if offsets are monotonically increasing
4. validate each slot.

What will be impacted?

1. We hope the validation could be somewhat faster (we need the benchmark result)
2. The Error message will change for some test cases. For example, given an offset buffer

[0, 1, 6, 3, 4, 5]

and offset_limit == 5
We will get an error "Offset invariant failure: offset at position 2 out of bounds: 6 > 5" now, but
Offset invariant failure: non-monotonic offset at slot 2: 6 > 3 if we do the simplification.

[HaoYang670]

I have done the simplification but no obvious performance improvement is gotten.
So close this issue