### What this PR does / why we need it?
The reason why we cannot use `self.cudagraph_batch_sizes[-1]` is that
it's actually not the max number of tokens to be padded in
`FULL_DECODE_ONLY` mode, much larger instead. And it's trimmed only
before capturing to `compilation_cases`, this really caused us lots of
trouble.
Updates the logic to ensure padding occurs only when the number of input
tokens falls within a valid uniform decode query range, improving
consistency and avoiding unnecessary padding in specific decode modes.
### Does this PR introduce _any_ user-facing change?
None.
### How was this patch tested?
None.
- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c
Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>
ff3914e31a