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.

crates/irtt-app/Cargo.toml

@@ -0,0 +1,62 @@
+[package]
+name = "irtt-rs"
+version = "0.6.0"
+description = "IRTT-compatible client, TUI, and server applications"
+edition.workspace = true
+license.workspace = true
+rust-version.workspace = true
+repository.workspace = true
+homepage.workspace = true
+readme.workspace = true
+keywords = ["irtt", "networking", "latency", "rtt"]
+categories = ["command-line-utilities", "network-programming"]
+
+[lib]
+name = "irtt_app"
+doc = false
+
+[[bin]]
+name = "irtt-rs"
+path = "src/bin/irtt-rs.rs"
+
+[[bin]]
+name = "irtt-client"
+path = "src/bin/irtt-client.rs"
+required-features = ["client"]
+# This applet shares its name with the irtt-client library crate, whose rustdoc
+# output it would otherwise collide with.
+doc = false
+
+[[bin]]
+name = "irtt-tui"
+path = "src/bin/irtt-tui.rs"
+required-features = ["tui"]
+
+[[bin]]
+name = "irtt-server"
+path = "src/bin/irtt-server.rs"
+required-features = ["server"]
+# This applet shares its name with the irtt-server library crate, whose rustdoc
+# output it would otherwise collide with.
+doc = false
+
+[features]
+default = ["client", "server", "tui"]
+client = ["dep:irtt-client", "irtt-client/ancillary", "irtt-client/tokio", "dep:irtt-proto", "dep:irtt-stats"]
+server = ["dep:irtt-server", "dep:tokio"]
+tui =["dep:irtt-client", "irtt-client/ancillary", "irtt-client/tokio", "dep:irtt-proto", "dep:irtt-stats", "dep:ratatui", "dep:crossterm"]
+
+[dependencies]
+clap = { version = "4.6.6", features = ["derive"] }
+crossterm = { version = "0.29.0", optional = true }
+ctrlc = "3.5.2"
+irtt-client = { workspace = true, optional = true }
+irtt-proto = { workspace = true, optional = true }
+irtt-server = { workspace = true, optional = true }
+irtt-stats = { workspace = true, optional = true }
+ratatui = { version = "0.30.2", optional = true }
+tokio = { version = "1.53.1", default-features = false, features = ["rt", "time"], optional = true }
+
+[dev-dependencies]
+irtt-server.workspace = true
+tokio = { version = "1.53.1", default-features = false, features = ["rt", "sync"] }