refactor: begin restructuring core code to better encapsulate

This is a first pass towards trying to structure things a bit better, with data generally encapsulated under a single hierarchical tree, rather than lots of globals all over the place. Lots of work is still required.

The plan is that with this and some more work, #291 should become a lot easier to sort.

src/cli.rs

@@ -0,0 +1,19 @@
+use crate::ipc::commands::Command;
+use crate::ipc::responses::Response;
+use clap::Parser;
+use serde::{Deserialize, Serialize};
+
+#[derive(Parser, Debug, Serialize, Deserialize)]
+#[command(version)]
+pub struct Args {
+    #[command(subcommand)]
+    pub command: Option<Command>,
+}
+
+pub fn handle_response(response: Response) {
+    match response {
+        Response::Ok => println!("ok"),
+        Response::OkValue { value } => println!("ok\n{value}"),
+        Response::Err { message } => eprintln!("error\n{}", message.unwrap_or_default()),
+    }
+}