fix codeql warnings and notes

[jlaehne]

Description of the change

Fixes warnings and notes from CodeQL scan: https://github.com/LumiSpy/lumispy/runs/9372886548

• avoid loading files without closing
• remove unused import
• remove commented-out code.

Progress of the PR

• [x] Change implemented (can be split into several points),
• [x] ready for review.

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (1ed2791) compared to base (da723d8). Patch coverage: 100.00% of modified lines in pull request are covered.

:exclamation: Current head 1ed2791 differs from pull request most recent head 68bfbc0. Consider uploading reports for the commit 68bfbc0 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #162 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 11 11 Lines 548 548 ========================================= Hits 548 548 ``` | [Impacted Files](https://codecov.io/gh/LumiSpy/lumispy/pull/162?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy) | Coverage Δ | | |---|---|---| | [lumispy/utils/axes.py](https://codecov.io/gh/LumiSpy/lumispy/pull/162/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy#diff-bHVtaXNweS91dGlscy9heGVzLnB5) | `100.00% <ø> (ø)` | | | [lumispy/signals/cl\_spectrum.py](https://codecov.io/gh/LumiSpy/lumispy/pull/162/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy#diff-bHVtaXNweS9zaWduYWxzL2NsX3NwZWN0cnVtLnB5) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LumiSpy)

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[jordiferrero]

Can you quickly solve the conflict. It's just the docs-fix you made in #163