Prevents unnecessary repeated search for well starting date

[edubarrosTNO]

Prevents unnecessary repeated search for well starting date inside for-loop when processing historical schedule production data

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Contributor checklist

• [x] :tada: This PR closes #439.
• [x] :scroll: I have broken down my PR into the following tasks:
  • [x] Removed search for well starting date from inside for-loop
• [ ] :robot: I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR.
• [x] :book: I have considered adding a new entry in CHANGELOG.md.
• [x] :books: I have considered updating the documentation.

[edubarrosTNO]

Adding new tests not applicable in this PR