Make sure One Shot Optimizer always returns the same suggestion (#759)

Make sure the `OneShotOptimizer.suggest()` call always returns the same
configuration.

Changes related to `MockEnv` determinism moved to #769 

Closes #755

---------

Co-authored-by: Brian Kroth <bpkroth@users.noreply.github.com>

mlos_bench/mlos_bench/optimizers/one_shot_optimizer.py

@@ -18,7 +18,7 @@
 
 class OneShotOptimizer(MockOptimizer):
  """
- Mock optimizer that proposes a single configuration and returns.
+ No-op optimizer that proposes a single configuration and returns.
  Explicit configs (partial or full) are possible using configuration files.
  """
 
@@ -33,6 +33,14 @@ def __init__(self,
  _LOG.info("Run a single iteration for: %s", self._tunables)
  self._max_iter = 1 # Always run for just one iteration.
 
+ def suggest(self) -> TunableGroups:
+ """
+ Always produce the same (initial) suggestion.
+ """
+ tunables = super().suggest()
+ self._start_with_defaults = True
+ return tunables
+
  @property
  def supports_preload(self) -> bool:
  return False