add flush for trace handler, will need to add for CPU

src/trace/file.rs

@@ -1,14 +1,17 @@
 use crate::trace::{CpuTrace, TraceHandler};
-use std::{fs::File, io::Write};
+use std::{
+  fs::File,
+  io::{BufWriter, Write},
+};
 
 pub struct FileTraceHandler {
-  file: File,
+  file: BufWriter<File>,
 }
 
 impl FileTraceHandler {
   pub fn new(filename: String) -> Self {
     Self {
-      file: File::create(filename).expect("Invalid filename"),
+      file: BufWriter::new(File::create(filename).expect("Invalid filename")),
     }
   }
 }
@@ -20,4 +23,8 @@ impl TraceHandler for FileTraceHandler {
       .write_all(format!("{:04X}: {:02X}\n", trace.address, trace.opcode).as_bytes())
       .unwrap();
   }
+
+  fn flush(&mut self) -> Result<(), &str> {
+    self.file.flush().map_err(|_| "failed to flush file")
+  }
 }

src/trace/mod.rs

@@ -11,4 +11,7 @@ pub struct CpuTrace {
 pub trait TraceHandler {
   /// Handle a trace event.
   fn handle(&mut self, trace: &CpuTrace);
+
+  /// Flush any existing resource buffers.
+  fn flush(&mut self) -> Result<(), &str>{ Ok(())}
 }