refactor(cli): separate binary entry points from library logic

Move the main execution logic to a dedicated internal module and create distinct entry files for each binary to improve project structure and build configuration.

crates/irtt-cli/src/bin/irtt-cli.rs

@@ -0,0 +1,5 @@
+use std::process::ExitCode;
+
+fn main() -> ExitCode {
+    irtt_cli::entry::main()
+}

crates/irtt-cli/src/bin/irtt-rs.rs

@@ -0,0 +1,5 @@
+use std::process::ExitCode;
+
+fn main() -> ExitCode {
+    irtt_cli::entry::main()
+}

crates/irtt-cli/src/bin/irtt-tui.rs

@@ -0,0 +1,5 @@
+use std::process::ExitCode;
+
+fn main() -> ExitCode {
+    irtt_cli::entry::main()
+}