Nevergrad Sweeper search-space configuration

Hydra 1.4 standardizes the Nevergrad Sweeper search-space configuration under hydra.sweeper.params. The previous hydra.sweeper.parametrization field is deprecated in Hydra 1.4 and will be removed in Hydra 1.5.

Move each search-space entry to params and express it using Hydra's override grammar:

hydra:
  sweeper:
    params:
      db: choice(mnist, cifar)
      lr: {init: 0.02, step: 2.0, log: true}
      dropout: interval(0, 1)
      batch_size: int(interval(4, 16))

The old configuration continues to work in Hydra 1.4 and emits a deprecation warning. Configuring both fields at the same time is an error.

See the Nevergrad Sweeper documentation for the complete search-space syntax.