[code][fix] improvements for LAN 202503

- more robust client <-> server connection
  - new client event: DownloadGameFilesFailed
  - 3 seconds to reconnect
  - retry forever if server is gone and never lose a UI request

- code cleanup here and there (mostly server)

crates/lanspread-server/Cargo.toml

@@ -21,8 +21,10 @@ lanspread-utils = { path = "../lanspread-utils" }
 
 # external
 bytes = { workspace = true }
+chrono = { workspace = true }
 clap = { workspace = true }
 eyre = { workspace = true }
+gethostname = { workspace = true }
 itertools = { workspace = true }
 s2n-quic = { workspace = true }
 serde_json = { workspace = true }
@@ -30,4 +32,5 @@ semver = { workspace = true }
 tokio = { workspace = true }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
+uuid = { workspace = true }
 walkdir = { workspace = true }