Closes #14132

Refactored the importDatabase() method in OvidImporter by extracting four private helper methods (parseField(), parseSource(), normalizeContributors(), and resolveEntryType()). This improves code readability and maintainability by reducing the method from 135 lines to 25 lines while preserving all existing functionality. All existing tests pass without modification.

Steps to test

Run the existing OvidImporter tests: ./gradlew :jablib:test --tests OvidImporterTest. All 236 tests should pass, confirming the refactoring maintains the original behavior.

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [/] I manually tested my changes in running JabRef (always required)
• [/] I added JUnit tests for changes (if applicable)
• [/] I added screenshots in the PR description (if change is visible to the user)
• [/] I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• [/] I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.