MHR - API Update Staff Serial Number Search (currently wildcard)

From OPs ticket https://sbc-registries.atlassian.net/browse/ITOPS-228457

Defined requirements and update MHR staff search by serial number - they do not like the current wildcard searching.

Requirements based on feedback from the business includes:

- The search process returns all records connected to an entered serial number (which could also be a partial serial number), including records stored in both modern and legacy sources.
- The search process returns the same results from both the legacy platform and the modern.
- The search process must not exclude any serial number record already confirmed to exist within legacy data stores.
- The search process retrieves partial serial number matches only when the full serial number is not available in the submitted data.
- The search process returns results in a consistent structure so staff understand the status of each returned record.
- The search process presents an error when no matching record exists in either system.

The need was stated for the modern serial number search to match legacy behavior to avoid missing records, and the gap was identified as an operational risk for staff who rely on complete results.
Please refer to #31866 for some more background on this