fix(bench): --ssh-host depth suite — create the remote scratch dir before cd

The depth suite uses a separate remote scratch dir ({stem}_depth) but only
the main scratch dir was created on the remote (prepare). The depth suite's
cd failed (no such dir) and the whole phase exited 127, so the deep-context
rows (16K-256K) were missing from the remote report. The remote command now
does mkdir -p <cwd> && cd <cwd> so both the main and the depth scratch dirs
are created on the remote host.

src/bench_remote.rs

@@ -15,7 +15,8 @@ use anyhow::Result;
 /// local run. The `cwd` is a remote path embedded in the shell string.
 pub fn remote_command(host: &str, cwd: &Path, bin: &str, args: &[String]) -> Command {
     let remote = format!(
-        "cd '{}' || exit 127; stty -onlcr 2>/dev/null; TTY_COMPATIBLE=0 NO_COLOR=1 exec {} {}",
+        "mkdir -p '{}' && cd '{}' || exit 127; stty -onlcr 2>/dev/null; TTY_COMPATIBLE=0 NO_COLOR=1 exec {} {}",
+        cwd.display(),
         cwd.display(),
         bin,
         args.join(" ")