DEV-15815 Added dedupe function to spending_level_to_process validation

[gregrholden]

Description:

DEV-15815: Raw spending_level bypasses TinyShield, amplifies download work [f-7a786b75]
The /api/v2/download/search/ endpoint should handle duplicate values provided to the spending_level filter without generating multiple download files.

Technical Details:

The /download/v2/request_validations.py's SearchDownloadValidator class allows a user to pass a list of spending_level values in their request for files to download, but the list is never deduplicated. A single request could therefore result in the same download file being generated multiple times, unnecessarily increasing the load on the system's resources. The solution is to update the spending_level list prior to TinyShield validation so that the original values passed through the entire class are deduplicated from the start.

NOTE: A good amount of code was updated with uv run ruff format in the updated files.

Requirements for PR Merge:

1. Unit & integration tests updated
2. API documentation updated (examples listed below)
   1. API Contracts
   2. API UI
   3. Comments
3. Data validation completed (examples listed below)
   1. Does this work well with the current frontend? Or is the frontend aware of a needed change?
   2. Is performance impacted in the changes (e.g., API, pipeline, downloads, etc.)?
   3. Is the expected data returned with the expected format?
4. Appropriate Operations ticket(s) created
5. Jira Ticket(s)
   1. DEV-15815

Explain N/A in above checklist: