Remove 'Press any key to exit' in basic-rs and basic-cpp templates (#4468)

The basic-rs and basic-cpp templates say "Press any key to exit..." but
stdin is line-buffered in cooked mode, so `read(&mut [0u8])` actually
blocks until Enter is pressed.

Adding a real "any key" handler would require a terminal crate
dependency (crossterm, termion, etc.) which is heavy for a starter
template. Instead, change the message to "Press Enter to exit..." and
use `read_line()` to match the actual behavior.

Also removes the unused `Read` import.

Co-authored-by: clockwork-labs-bot <clockwork-labs-bot@users.noreply.github.com>
Co-authored-by: Zeke Foppa <196249+bfops@users.noreply.github.com>

Author: clockwork-labs-bot

templates/basic-cpp/src/main.rs

@@ -1,7 +1,6 @@
 mod module_bindings;
 use module_bindings::*;
 use std::env;
-use std::io::{self, Read};
 
 use spacetimedb_sdk::{DbContext, Table};
 
@@ -40,7 +39,8 @@ fn main() {
         println!("New person: {}", person.name);
     });
 
-    println!("Press any key to exit...");
-
-    let _ = io::stdin().read(&mut [0u8]).unwrap();
+    // Keep the main thread alive so the connection stays open
+    loop {
+        std::thread::sleep(std::time::Duration::from_secs(1));
+    }
 }

templates/basic-rs/src/main.rs

@@ -1,7 +1,6 @@
 mod module_bindings;
 use module_bindings::*;
 use std::env;
-use std::io::{self, Read};
 
 use spacetimedb_sdk::{DbContext, Table};
 
@@ -40,7 +39,8 @@ fn main() {
         println!("New person: {}", person.name);
     });
 
-    println!("Press any key to exit...");
-
-    let _ = io::stdin().read(&mut [0u8]).unwrap();
+    // Keep the main thread alive so the connection stays open
+    loop {
+        std::thread::sleep(std::time::Duration::from_secs(1));
+    }
 }