refactor(pageserver): propagate RequestContext to layer downloads (#11001)

For some reason the layer download API never fully got
`RequestContext`-infected.

This PR fixes that as a precursor to
- https://github.com/neondatabase/neon/issues/6107

pageserver/compaction/src/compact_tiered.rs

@@ -307,7 +307,7 @@ where
                 let mut layer_ids: Vec<LayerId> = Vec::new();
                 for layer_id in &job.input_layers {
                     let layer = &self.layers[layer_id.0].layer;
-                    if let Some(dl) = self.executor.downcast_delta_layer(layer).await? {
+                    if let Some(dl) = self.executor.downcast_delta_layer(layer, ctx).await? {
                         deltas.push(dl.clone());
                         layer_ids.push(*layer_id);
                     }
@@ -536,7 +536,7 @@ where
         let mut deltas: Vec<E::DeltaLayer> = Vec::new();
         for layer_id in &job.input_layers {
             let l = &self.layers[layer_id.0];
-            if let Some(dl) = self.executor.downcast_delta_layer(&l.layer).await? {
+            if let Some(dl) = self.executor.downcast_delta_layer(&l.layer, ctx).await? {
                 deltas.push(dl.clone());
             }
         }

pageserver/compaction/src/interface.rs

@@ -55,6 +55,7 @@ pub trait CompactionJobExecutor {
     fn downcast_delta_layer(
         &self,
         layer: &Self::Layer,
+        ctx: &Self::RequestContext,
     ) -> impl Future<Output = anyhow::Result<Option<Self::DeltaLayer>>> + Send;
 
     // ----

pageserver/compaction/src/simulator.rs

@@ -487,6 +487,7 @@ impl interface::CompactionJobExecutor for MockTimeline {
     async fn downcast_delta_layer(
         &self,
         layer: &MockLayer,
+        _ctx: &MockRequestContext,
     ) -> anyhow::Result<Option<Arc<MockDeltaLayer>>> {
         Ok(match layer {
             MockLayer::Delta(l) => Some(l.clone()),