Gap filling with NaN values added to Level 2

[ladsmund]

Context:

This pull request supersedes PR #283, which was automatically closed due to the deletion of the develop branch. The bugfix/level_2_data_gaps branch has been rebased onto main, and this new PR is being submitted to continue the integration process.

Summary of Original PR (#283):

• Title: Gap filling with NaN values added to Level 2
• Description: Introduced a gap-filling step ensuring that Level 2 data no longer contains gaps. Specifically:
  • Determined the datetime range of the dataset.
  • Identified the most common time interval (e.g., 10 minutes, hourly).
  • Generated an index without gaps.
  • Reindexed the dataset accordingly.

For a detailed view of the original changes and discussions, please refer to PR #283.