main: Move logger into its own mod

In preparation for extending its functionality, refactor the Logger
struct and its implementation to a new file / module.

Assisted-by: Claude:Opus-4.6
Signed-off-by: Rob Bradford <rbradford@meta.com>

cloud-hypervisor/src/logger.rs

@@ -0,0 +1,47 @@
+// Copyright © 2026 Cloud Hypervisor Contributors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+use std::sync::Mutex;
+
+pub struct Logger {
+    pub output: Mutex<Box<dyn std::io::Write + Send>>,
+    pub start: std::time::Instant,
+}
+
+impl log::Log for Logger {
+    fn enabled(&self, _metadata: &log::Metadata) -> bool {
+        true
+    }
+
+    fn log(&self, record: &log::Record) {
+        if !self.enabled(record.metadata()) {
+            return;
+        }
+
+        let now = std::time::Instant::now();
+        let duration = now.duration_since(self.start);
+        let duration_s = duration.as_secs_f32();
+
+        let location = if let (Some(file), Some(line)) = (record.file(), record.line()) {
+            format!("{file}:{line}")
+        } else {
+            record.target().to_string()
+        };
+
+        let mut out = self.output.lock().unwrap();
+        write!(
+            &mut *out,
+            // 10: 6 decimal places + sep => whole seconds in range `0..=999` properly aligned
+            "cloud-hypervisor: {:>10.6?}s: <{}> {}:{} -- {}\r\n",
+            duration_s,
+            std::thread::current().name().unwrap_or("anonymous"),
+            record.level(),
+            location,
+            record.args(),
+        )
+        .ok();
+    }
+    fn flush(&self) {}
+}