chore(test): Adopt Gherkin-style notation for DataIngestorTest readability

[impatient0]

Summary

This pull request refactors the test structure and naming conventions within DataIngestorTest to adopt the Gherkin-style notation (Given/When/Then), aligning it with the pattern established in the BacktestEngineTest class.

Key Changes

• Test Structure: Introduces a top-level @Nested class with a GIVEN block (GIVEN DataIngestor is configured to fetch Klines data) to group related tests.
• Readability: Updates individual @DisplayName annotations for test methods to follow the WHEN... THEN... structure, significantly improving the clarity of the test specification.
• Scope: This is a purely cosmetic and structural refactoring of the test class. No changes have been made to the underlying test logic, assertions, or production code, ensuring full backward compatibility and correctness.

This change promotes a unified and highly readable test standard across the project.