pageserver: handle temp_download files in secondary locations (#6990)

## Problem

PR #6837 fixed secondary locations to avoid spamming log warnings on
temp files, but we also have ".temp_download" files to consider.

## Summary of changes

- Give temp_download files the same behavior as temp files.
- Refactor the relevant helper to pub(crate) from pub

pageserver/src/tenant/remote_timeline_client/download.rs

@@ -161,7 +161,7 @@ pub async fn download_layer_file<'a>(
 
 const TEMP_DOWNLOAD_EXTENSION: &str = "temp_download";
 
-pub fn is_temp_download_file(path: &Utf8Path) -> bool {
+pub(crate) fn is_temp_download_file(path: &Utf8Path) -> bool {
     let extension = path.extension();
     match extension {
         Some(TEMP_DOWNLOAD_EXTENSION) => true,

pageserver/src/tenant/secondary/downloader.rs

@@ -16,7 +16,8 @@ use crate::{
         config::SecondaryLocationConfig,
         debug_assert_current_span_has_tenant_and_timeline_id,
         remote_timeline_client::{
-            index::LayerFileMetadata, FAILED_DOWNLOAD_WARN_THRESHOLD, FAILED_REMOTE_OP_RETRIES,
+            index::LayerFileMetadata, is_temp_download_file, FAILED_DOWNLOAD_WARN_THRESHOLD,
+            FAILED_REMOTE_OP_RETRIES,
         },
         span::debug_assert_current_span_has_tenant_id,
         storage_layer::LayerFileName,
@@ -788,7 +789,7 @@ async fn init_timeline_state(
             // Secondary mode doesn't use local metadata files, but they might have been left behind by an attached tenant.
             warn!(path=?dentry.path(), "found legacy metadata file, these should have been removed in load_tenant_config");
             continue;
-        } else if crate::is_temporary(&file_path) {
+        } else if crate::is_temporary(&file_path) || is_temp_download_file(&file_path) {
             // Temporary files are frequently left behind from restarting during downloads
             tracing::info!("Cleaning up temporary file {file_path}");
             if let Err(e) = tokio::fs::remove_file(&file_path)