fix: set transfer from and to stop ids as conditional required fields

[davidgamez]

Summary:

This PR aligns the validator response with the specification on the transfers.txt from and to stop IDs. The specification marks these fields as required for all records except those with a transfer_type of 4 or 5.

Closes #1621

Expected behavior:

For transfers.txt records with transfer types 4 and 5(in seat transfer types), the missing required field is not triggered.

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[github-actions]

✅ Rule acceptance tests passed.
New Errors: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
Dropped Errors: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
New Warnings: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
Dropped Warnings: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
0 out of 1523 sources (~0 %) are corrupted.
Commit: 7e6ac69
Download the full acceptance test report here (report will disappear after 90 days).
✅ Rule acceptance tests passed.

[qcdyx]

LGTM

[github-actions]

✅ Rule acceptance tests passed.
New Errors: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
Dropped Errors: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
New Warnings: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
Dropped Warnings: 0 out of 1523 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
0 out of 1523 sources (~0 %) are corrupted.
Commit: cb45764
Download the full acceptance test report here (report will disappear after 90 days).
✅ Rule acceptance tests passed.