Add upsert Method

[teles]

Add upsert Method

Description:

Introduce the upsert method to enable updating an existing record or inserting a new one if it does not exist, combining the functionalities of update and insert operations.

Objective:

• Implement the upsert method that accepts parameters to identify the record and the data to update or insert.
• Ensure the method performs the operation atomically.
• Maintain data integrity during the operation.

Acceptance Criteria:

• Calling upsert({ where: { id: 1 }, update: { ... }, data: { ... } }) updates the existing record.
• Calling upsert({ where: { id: 999 }, update: { ... }, data: { ... } }) inserts a new record when no match is found.
• Documentation and usage examples are included.
• Automated tests cover both update and insert scenarios.

[teles]

No progress yet

No upsert method exists anywhere in the codebase.

❌ Still needed: Implement upsert(options) — finds a record matching the where clause and updates it if found, or inserts it if not. Could live in a new WithUpsertOperations mixin or be added to WithUpdateOperations.