chore(spec): little refacto on the spec to simplify further migration

Author: SouchonTheo

utils/benchmark_spec/src/csv_writer.rs

@@ -0,0 +1,36 @@
+//! Appends benchmark results to a CSV file.
+
+use std::fs::{File, OpenOptions};
+use std::io::Write;
+use std::path::Path;
+
+pub struct CsvResultWriter {
+    file: File,
+}
+
+impl CsvResultWriter {
+    pub fn new(file_name: &str) -> Self {
+        let file_path = Path::new(file_name);
+        Self::from_path(file_path)
+    }
+
+    pub fn from_path(path: &Path) -> Self {
+        if !path.exists() {
+            if let Some(parent) = path.parent() {
+                std::fs::create_dir_all(parent).expect("cannot create parent dirs");
+            }
+            File::create(path).expect("cannot create result file");
+        }
+        let file = OpenOptions::new()
+            .append(true)
+            .open(path)
+            .expect("cannot open result file");
+        Self { file }
+    }
+
+    pub fn write_result(&mut self, name: &str, value: usize) {
+        let line = format!("{name},{value}\n");
+        let error_message = format!("cannot write {name} result into file");
+        self.file.write_all(line.as_bytes()).expect(&error_message);
+    }
+}