Fix/algos

[belerico]

Summary

In this PR we have fixed multiple minor bugs, i.e.:

• Reshape the image observations when bootstrapping in all the PPO algorithms
• The image normalization is carried out by / 255.0 - 0.5 in all the PPO algorithms
• Prevent saving the "observations" keys in P2E-DV1
• Fix metrics when they are nan
• Log timer metrics only if times have been measured

Type of Change

Please select the one relevant option below:

• Bug fix (non-breaking change that solves an issue)

Checklist

Please confirm that the following tasks have been completed:

• I have tested my changes locally and they work as expected. (Please describe the tests you performed.)
• I have added unit tests for my changes, or updated existing tests if necessary.
• I have updated the documentation, if applicable.
• I have installed pre-commit and run locally for my code changes.

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