Fix dangling pointer in TextTokenGenerator non-kv-cache path

Summary:
In the non-kv-cache branch of TextTokenGenerator::generate(), push_back()
on token_data can trigger vector reallocation, but the tensor created via
from_blob still points to the old data address. resize_tensor_ptr only
updates shape metadata, not the data pointer, resulting in a dangling
pointer.

Fix by pre-allocating the vector with reserve() before creating the
tensor, ensuring push_back never triggers reallocation during the
generate loop.

Differential Revision: D99408541

Author: kirklandsign

extension/llm/runner/text_token_generator.h

@@ -77,6 +77,8 @@ class ET_EXPERIMENTAL TextTokenGenerator {
     } else {
       token_data = tokens;
       token_shape = {1, static_cast<int>(tokens.size())};
+      // Prevent reallocation that would invalidate from_blob's data pointer.
+      token_data.reserve(token_data.size() + max_new_tokens);
     }
 
     // initialize tensor wrappers