fix(output): align TSV rows to block headers

[Athemis]

Summary

• Fix TSV row generation so values are written in final header order.
• Preserve empty cells for missing optional fields to keep later columns aligned.
• Add regression coverage for mixed YAML key order within one block.

Closes #31

[HenningTimm]

Thank you! Is it intentional that the displayFormat entry for the First entry is missing? This seems to mess up the column order of the generated TSV, but this unrelated to this PR.

[Athemis]

Thank you! Is it intentional that the displayFormat entry for the First entry is missing? This seems to mess up the column order of the generated TSV, but this unrelated to this PR.

That's intentional: With this PR merged, all entries should be taken into account regardless whether they are present in the first or any other item. That's what the test checks for: Are all entries included in the final tsv output even if they are not all present in the first item.