[vLLM] Hoist TT attention batch metadata out of the compiled graph

[mmanzoorTT]

Ticket

closes #5154

Problem description

Batch index are generated for each prefill call

What's changed

• Hoist batch index creation to runner constructer.
• Add num_user to attn_metadata and use it directly instead of deducing it

Checklist

• New/Existing tests provide coverage for changes

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 33.83%. Comparing base (b621dab) to head (2732f60).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5485      +/-   ##
==========================================
- Coverage   33.85%   33.83%   -0.03%     
==========================================
  Files          37       37              
  Lines        4989     4989              
==========================================
- Hits         1689     1688       -1     
- Misses       3300     3301       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.