io/storage: split out inner part of read/write

Allow reusing the read/write logic without requiring control over the file
open.

src/core/region_processor.rs

@@ -145,7 +145,7 @@ impl<'a> SingleRegionProcessor<'a> {
 			return Ok(());
 		}
 
-		storage::write(
+		storage::write_file(
 			&self.output_path,
 			&self.processed_region,
 			REGION_FILE_META_VERSION,

src/core/tile_renderer.rs

@@ -105,7 +105,7 @@ impl<'a> TileRenderer<'a> {
 
 		region_loader
 			.get_or_try_init(|| async {
-				storage::read(&processed_path).context("Failed to load processed region data")
+				storage::read_file(&processed_path).context("Failed to load processed region data")
 			})
 			.await
 			.cloned()