hello_world need to get updated

1. The current default cmake configuration file causes "gemma/gemma.h" and several other header files to be missing.
2. Attempting to use the deleted constructor gcpp::NestedPools::NestedPools(gcpp::NestedPools &&) and gcpp::Gemma::Gemma(const gcpp::Gemma &)
3. gcpp::RuntimeConfig runtime_config has problem, because the definition changed.

Start with the default CMake configuration used by hello_world and compare its generated include availability with the headers named in the issue. Then inspect the current NestedPools, Gemma, and RuntimeConfig declarations and update hello_world for the current interfaces; done means it configures and builds without missing headers or deleted-constructor and RuntimeConfig errors.

Written by the indexing model from the issue text.