Add emit_result_slice_pointer option for :many queries

[Alexfilus]

Summary

• Adds new emit_result_slice_pointer option that changes :many query signature to accept a destination slice pointer instead of returning a new slice
• When enabled, generated functions use func(..., dest *[]T) error instead of func(...) ([]T, error)
• This optimization eliminates allocations by allowing callers to reuse pre-allocated slices

Example

Default behavior (emit_result_slice_pointer: false):

func (q *Queries) GetItems(ctx context.Context, ids []string) ([]Item, error)

With emit_result_slice_pointer: true:

func (q *Queries) GetItems(ctx context.Context, ids []string, dest *[]Item) error

Changes

• internal/opts/options.go: Added EmitResultSlicePointer option
• internal/gen.go: Wired option to template context
• internal/templates/pgx/queryCode.tmpl: Added conditional template for new behavior

Test plan

• Built with make all
• Ran make test - all tests pass
• Tested locally with real sqlc project

🤖 Generated with Claude Code