refactor(app): clarify application and binary roles

Rename the application Cargo package from irtt-cli to irtt-rs
(crates/irtt-cli -> crates/irtt-app), and hard-rename its scriptable
client binary from irtt-cli to irtt-client, now that the application
also ships a first-class server and the old name reads as an umbrella
CLI for both roles.

Give each dedicated binary (irtt-client, irtt-tui, irtt-server) its
own entry point instead of funneling through the multicall
dispatcher's argv0/subcommand logic, so a dedicated binary only links
the applet code for the role it implements and always runs that role
regardless of the name it's invoked or copied under. irtt-rs remains
the feature-selectable multicall dispatcher and is now the only binary
that inspects argv0 or subcommands.

Move future application releases to the irtt-rs/vX.Y.Z tag namespace
(regenerated via `dist generate`), and bump the application package to
0.6.0 as a breaking distribution change. Library crate versions are
unaffected.

.github/workflows/interop-netem.yml

@@ -46,8 +46,8 @@ jobs:
           go install "github.com/heistp/irtt/cmd/irtt@${IRTT_UPSTREAM_VERSION}"
           "$GOBIN/irtt" version
 
-      - name: Build irtt-rs CLI
-        run: cargo build -p irtt-cli --locked
+      - name: Build irtt-rs client
+        run: cargo build -p irtt-rs --bin irtt-client --locked
 
       - name: Run netem interop comparisons
         run: |
@@ -55,7 +55,7 @@ jobs:
             --all \
             --skip-build \
             --upstream-irtt "$GOBIN/irtt" \
-            --irtt-rs-command "$PWD/target/debug/irtt-cli"
+            --irtt-rs-command "$PWD/target/debug/irtt-client"
 
       - name: Append netem interop summary
         if: always()