Default to puffin venv path to .venv (#261)

Closes https://github.com/astral-sh/puffin/issues/236

crates/puffin-cli/src/main.rs

@@ -147,6 +147,7 @@ struct VenvArgs {
     python: Option<PathBuf>,
 
     /// The path to the virtual environment to create.
+    #[clap(default_value = ".venv")]
     name: PathBuf,
 }
 

crates/puffin-cli/tests/snapshots/venv__create_venv_defaults_to_cwd.snap

@@ -0,0 +1,15 @@
+---
+source: crates/puffin-cli/tests/venv.rs
+info:
+  program: puffin
+  args:
+    - venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Using Python interpreter: /usr/bin/python3
+Creating virtual environment at: .venv
+

crates/puffin-cli/tests/venv.rs

@@ -30,3 +30,24 @@ fn create_venv() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn create_venv_defaults_to_cwd() -> Result<()> {
+    let tempdir = assert_fs::TempDir::new()?;
+    let venv = tempdir.child(".venv");
+
+    insta::with_settings!({
+        filters => vec![
+            (r"Using Python interpreter: .+", "Using Python interpreter: /usr/bin/python3"),
+            (tempdir.to_str().unwrap(), "/home/ferris/project"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("venv")
+            .current_dir(&tempdir));
+    });
+
+    venv.assert(predicates::path::is_dir());
+
+    Ok(())
+}