Fix N+1 Query Performance Issue in Vets Endpoint-created-by-agentic

[shaykeren]

This PR addresses the N+1 query performance issue in the Vets endpoint by:

1. Changing the fetch type from EAGER to LAZY in the Vet entity's specialties relationship
2. Adding @batchsize annotation to optimize batch loading
3. Implementing @entitygraph for efficient loading of specialties
4. Adding database indexes on vet_specialties.vet_id, vet_specialties.specialty_id, and specialties.id

These changes should significantly improve the performance of the /vets.html endpoint by reducing the number of database queries executed.