🐛🧪 cli, vanth: Fix SQLite store bug and add CLI tests

- Modified `Sqlite::get_all_of_ty` to return stored rows instead of empty results.
- Added `Send` requirement to `Backend` trait.
- Implemented `ContentHash::hex` method for hexadecimal representation.
- Added integration test for CLI `write` and `get` commands with `run_vanth` helper.
- Configured CLI tracing to log to stderr instead of stdout.
- Added `serde` dependency to `cli` crate for test struct serialization.
- Modified `handle_write` to print content hash after successful storage.

crates/cli/tests/integration/main.rs

@@ -0,0 +1,83 @@
+use std::io::Write;
+use std::path::Path;
+use std::process::Command;
+
+use serde::{Deserialize, Serialize};
+use serde_json::{Value, json};
+use tempfile::tempdir;
+use vanth::{ContentHash, Vanth, hash as vanth_hash};
+
+fn run_vanth(args: &[&str], input: Option<&str>) -> (String, String, i32) {
+    let mut cmd = Command::new(env!("CARGO_BIN_EXE_vanth_cli"));
+    cmd.args(args);
+    if let Some(inp) = input {
+        let mut child = cmd
+            .stdin(std::process::Stdio::piped())
+            .stdout(std::process::Stdio::piped())
+            .stderr(std::process::Stdio::piped())
+            .spawn()
+            .unwrap();
+        {
+            let stdin = child.stdin.as_mut().unwrap();
+            stdin.write_all(inp.as_bytes()).unwrap();
+        }
+        let output = child.wait_with_output().unwrap();
+        (
+            String::from_utf8(output.stdout).unwrap(),
+            String::from_utf8(output.stderr).unwrap(),
+            output.status.code().unwrap(),
+        )
+    } else {
+        let output = cmd.output().unwrap();
+        (
+            String::from_utf8(output.stdout).unwrap(),
+            String::from_utf8(output.stderr).unwrap(),
+            output.status.code().unwrap(),
+        )
+    }
+}
+
+#[derive(Clone, Debug, Deserialize, PartialEq, Serialize, Vanth)]
+struct Foo {
+    inner: i32,
+}
+
+#[derive(Clone, Debug, Deserialize, Serialize, Vanth)]
+struct Bar {
+    inner: f64,
+}
+
+/// Create a value in the database with the `write` command, gets its hash from the CLI stdout output, and retrieve it
+/// again with the `get` command.
+#[test]
+fn test_write_get() {
+    let tempdir = tempdir().unwrap();
+    let db_path = tempdir.path().join("test.sqlite").to_str().unwrap().to_string();
+
+    let foo = Foo { inner: 6 };
+
+    let (stdout, stderr, exit) = run_vanth(
+        &[
+            "write",
+            "--db",
+            &db_path,
+            "--ty",
+            &Foo::ty().to_string(),
+            "--value",
+            &serde_json::to_string(&foo).unwrap(),
+        ],
+        None,
+    );
+    if exit != 0 {
+        panic!("{}", stderr);
+    }
+    let hash = stdout.trim();
+    println!("x{}x", hash);
+
+    let (stdout, stderr, exit) = run_vanth(&["get", "--db", &db_path, "--ty", &Foo::ty().to_string(), &hash], None);
+    if exit != 0 {
+        panic!("{}", stderr);
+    }
+    let recovered_foo = serde_json::from_str(&stdout).unwrap();
+    assert_eq!(foo, recovered_foo);
+}