Address ANAPIC review comments -- hal.

- Document that IPreparedModel::execute*WithConfig are for single-time
  usages, and IPreparedModel::createReusableExecution is for reusable
  usages.
- Make PrepareModelConfig::cacheToken a fixed sized array.

Fixes: 215566186
Test: VtsHalNeuralnetworksTargetTest
Test: NNT_static
Change-Id: I9c5a49c46a3eac2828b9eb666f3d742038493121