🐛 Fix pipeline order in mount_base_pipeline

[patrickpasquini]

This PR fixes the pipeline stage ordering in the mount_base_pipeline function when populate=True. The reference stage was being placed after sort, skip, and limit stages, which could lead to incorrect query results.

Changes

• Move reference_stage to execute before sort_stage, skip_stage, and limit_stage in the pipeline
• This ensures population of references happens before sorting and pagination operations

Why this matters

The previous order could cause issues when:

• Sorting by fields from populated references
• The populated data affects the sorting