misc: enhance allocator error info and add shape check for prefill begin forward functions

[yzh119]

This PR makes the following changes to the codebase:

1. make the allocators error information more informative, more specifically, we print the buffer name and requested buffer size in runtime errors for debugging.
2. add checks in prefill wrappers begin_forward functions to make sure qo and kv indptr array size matches.

These efforts are designed for avoiding issues such as #362 , which needs to be fixed on vllm side, but we should have more friendly debugging information for locating the potential bugs.