fix for issue #660 where the call to llama_batch_free is failing during process shutdown

[paulbkoch]

llama_batch_free is failing during python shutdown when the interpreter can set objects to None non-deterministically. I believe Guidance is properly checking for None in the objects that can be accessed from Guidance, but llama-cpp-python is not, and the native library object in llama-cpp-python is being set to None before it can be called. Since we're only dealing with memory deallocation here, and since the process is being killed anyway, we can solve this on the Guidance side by not calling llama_batch_free during process termination.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.57%. Comparing base (94744ea) to head (8665e75).
Report is 1 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #734      +/-   ##
==========================================
- Coverage   69.17%   65.57%   -3.60%     
==========================================
  Files          53       53              
  Lines        3951     3957       +6     
==========================================
- Hits         2733     2595     -138     
- Misses       1218     1362     +144     

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