Add `BadgerDBGetPipeline` method for `PipelineModel`

[jim-junior]

Description

Extend the PipelineModel struct by adding a new standalone query method called BadgerDBGetPipeline. To ensure backward compatibility across existing services and workers, do not refactor, rename, or drop the current etcd-based GetPipeline implementation. This method will introduce native support to fetch and unmarshal a specific pipeline configuration record directly from BadgerDB.

Requirements

• File Location: internal/models/pipeline.go
• Method Signature Strategy: Introduce a new method named BadgerDBGetPipeline(name string) (*types.Pipeline, error) on the PipelineModel struct.
• Transactionality: Execute the fetch operation inside a BadgerDB View (read-only) transaction.
• Key Generation: Calculate the target key using the established convention: /pipelines/{name}.
• Data Retrieval & Deserialization:
  • Query the item matching the formatted key inside the transaction boundary.
  • Safely unpack or copy the raw byte payload from the database item context (e.g., using item.ValueCopy()) to comply with BadgerDB's standard memory lifecycle constraints.
  • Use the standard json.Unmarshal package to deserialize the JSON bytes back into a native *types.Pipeline struct reference.
• Error Handling: If the target key does not exist inside BadgerDB (errors.Is(err, badger.ErrKeyNotFound)), bubble up a descriptive custom error: fmt.Errorf("pipeline not found") to guarantee strict error parity with the historical etcd implementation.
• Testing: Create a dedicated unit test case inside internal/models/pipeline_test.go to validate standalone dataset retrieval and missing key handling using an ephemeral, in-memory BadgerDB instance.

Success Criteria

• The BadgerDBGetPipeline method is added cleanly alongside legacy methods without altering current external structural signatures.
• The engine executes data queries inside a localized read-only View transaction.
• Requesting a non-existent pipeline identifier correctly surfaces the exact custom validation error: pipeline not found.
• Test Case implementation: A comprehensive unit test is provided that:
  • Seeds an isolated, in-memory BadgerDB database with a pre-marshaled JSON configuration for a pipeline mock object.
  • Successfully calls BadgerDBGetPipeline using the designated object name.
  • Asserts that the returned type object matches the seeded fields exactly.
  • Confirms that passing a non-existent name string triggers the matching "not found" error.