### What this PR does / why we need it?
When using multi connector, the multi connector does not define
get_finished_count, which will cause the kv cache to be released ###
Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.11.0rc3
- vLLM main:
83f478bb19
Signed-off-by: baxingpiaochong <771405853@qq.com>
Co-authored-by: baxingpiaochong <771405853@qq.com>