Add pre-commit hook to check json formatting

[ericpre]

Progress of the PR

• Add pre-commit hook to check formatting json,
• [n/a] docstring updated (if appropriate),
• [n/a] update user guide (if appropriate),
• [n/a] added tests,
• add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:exspy build of this PR (link in github checks)
• ready for review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.94%. Comparing base (65ad47e) to head (4972dcc).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
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  Coverage   88.94%   88.94%           
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  Files          77       77           
  Lines        7529     7529           
  Branches      896      896           
=======================================
  Hits         6697     6697           
  Misses        563      563           
  Partials      269      269           

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[Copilot]

Pull Request Overview

This PR adds a pre-commit hook to automatically format JSON files while also updating tests to reflect a change in the expected ordering of complementary edges and revising the JSON file structure.

• Added a new pre-commit hook configuration for pretty-formatting JSON files.
• Updated test assertions in test_eels.py and test_edges_range.py to reflect a revised ordering.
• Reordered the metadata section in elements_general_properties.json.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
upcoming_changes/128.maintenance.rst	Added changelog entry for the pre-commit hook update.
exspy/tests/signals/test_eels.py	Updated the ordering of expected complementary edges in tests.
exspy/tests/signals/test_edges_range.py	Updated the ordering of expected complementary edges in tests.
exspy/_misc/elements_general_properties.json	Reordered metadata placement and adjusted formatting in the JSON file.
.pre-commit-config.yaml	Added configuration for the pretty-format-json pre-commit hook.

[ericpre]

@francisco-dlp, what do you think about sorting the keys in the json files alphabetically that this PR introduces? On main, there are mostly sorted by energy, not always.