docs: format docstrings in utils.py

[bryzgin]

Description

This PR updates the docstrings in gemgis/utils.py to comply with the numpydoc standard, as requested in #352.

Key changes include:

• Replaced non-standard underscores (______) with standard dashes (------) in section headers.
• Fixed parameter formatting by adding colons between names and types (name : type).
• Added missing blank lines after summary descriptions to fix formatting errors.
• Improved indentation and consistency in the following functions:
  • to_section_dict
  • convert_to_gempy_df
  • set_extent

Relates to #352

Checklist

• My code follows the PEP 8 style guidelines.
• My code uses type hinting for function and method arguments and return values.
• My code contains descriptive and helpful docstrings
  which are formatted per the numpydoc Style Guidelines.
• I have created tests which entirely cover my code.
• The test code either 1. demonstrates at least one valuable use case (e.g. integration tests)
  or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
• New and existing tests pass locally with my changes.

[github-actions]

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