ENH: Using float converters on integer values

Summary

see https://gitlab.com/caosdb/caosdb-crawler/-/issues/10

Note, that I also introduced the registered integration tests.

Test Environment

unit und int tests

Check List for the Author

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• All automated tests pass
• Reference related issues
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• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
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