[Core] Fix block table shape to make Prefix cache work with Ascend scheduler

[yiz-liu]

What this PR does / why we need it?

This fix the shape of block_table which was introduced by hybrid kv groups several weeks ago.

Error will be raised when enable prefix-cache (eager or not) and Ascend Scheduler at the same time, just send two identical requests and it will reproduce.

Does this PR introduce any user-facing change?

How was this patch tested?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 27.41%. Comparing base (c30ddb8) to head (a37cce9).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
vllm_ascend/attention/attention_v1.py	0.00%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (100.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1446      +/-   ##
==========================================
+ Coverage   27.39%   27.41%   +0.01%     
==========================================
  Files          56       56              
  Lines        6191     6271      +80     
==========================================
+ Hits         1696     1719      +23     
- Misses       4495     4552      +57     

Flag	Coverage Δ
unittests	27.41% <0.00%> (+0.01%)	⬆️

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