Decouple DeadlineMovingAverageModel from PerSegmentModelMixin

[Mr-Geekman]

🚀 Feature Request

We want to uncouple DeadlineMovingAverageModel from PerSegmentModelMixin. Doing this, we can make DeadlineMovingAverageModel predict on any new segments because it doesn't require fit to work.

It also can lead to better performance.

Proposal

• Implement DeadlineMovingAverageModel without using PerSegmentModelMixin and NonPredictionIntervalContextRequiredModelMixin. It should be inherited only from NonPredictionIntervalContextRequiredAbstractModel.
• Method get_model should return self.
• Try to vectorize forecasting logic.

Test cases

1. Make sure current tests pass.
2. Adapt tests on _DeadlineMovingAverageModel.
3. Fix test_inference tests to work on new segments.

Additional context

No response

[Mr-Geekman]

Closed by #1140.