SSE-based directory size handling

This allows us to cancel stale clients and in general be much nicer and more modern.

Author: svenstaro

Cargo.lock

@@ -22,6 +22,7 @@ actix-files = "0.6.5"
 actix-multipart = "0.7"
 actix-web = { version = "4", features = ["macros", "compress-brotli", "compress-gzip", "compress-zstd"], default-features = false }
 actix-web-httpauth = "0.8"
+actix-web-lab = "0.24.0"
 alphanumeric-sort = "1"
 anyhow = "1"
 async-walkdir = "2.1.0"