chore: bump version to 0.4.0 across all workspace packages

Update the version of irtt-proto, irtt-client, irtt-stats, and irtt-cli to 0.4.0 in preparation for a new release.

crates/irtt-stats/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "irtt-stats"
-version = "0.3.0"
+version = "0.4.0"
 description = "Statistics aggregation for irtt-client events"
 edition.workspace = true
 license.workspace = true