Enhance logging and timing in CLI and session operations

- Updated the `_print_checks` function to replace console prints with logging functions for better traceability.
- Introduced timing functionality in the `doctor`, `dry_run`, and `up` functions to log the duration of preflight checks.
- Modified the `wait_ssh` function to accept a logging callback, improving SSH wait feedback.
- Enhanced the `mark` method in `PhaseTimes` to log phase durations, aiding in performance analysis.
- Updated various remote scripts to ensure error messages are printed to stderr for better error handling.

src/gpu_rent/ssh_ops.py

@@ -171,7 +171,12 @@ def probe_ssh(cfg: Config, host: str, attempts: int = 3) -> str:
     return "auth" if auth_seen else "down"
 
 
-def wait_ssh(cfg: Config, host: str, timeout: float = 900.0) -> None:
+def wait_ssh(
+    cfg: Config,
+    host: str,
+    timeout: float = 900.0,
+    log: Callable[[str], None] | None = None,
+) -> None:
     """Wait until sshd accepts our key. Paramiko banner noise is muted.
 
     AuthenticationException is normal while cloud-init injects keys: keep
@@ -183,6 +188,8 @@ def wait_ssh(cfg: Config, host: str, timeout: float = 900.0) -> None:
     logging.getLogger("paramiko").setLevel(logging.CRITICAL)
     logging.getLogger("paramiko.transport").setLevel(logging.CRITICAL)
 
+    emit = log if log is not None else print
+
     # sshd may answer before authorized_keys is ready (boot-from-volume / user_data).
     auth_give_up = 180.0
 
@@ -223,7 +230,7 @@ def wait_ssh(cfg: Config, host: str, timeout: float = 900.0) -> None:
             except Exception:
                 pass
             if attempt == 1 or attempt % 6 == 0:
-                print(f"жду SSH {cfg.ssh_user}@{host}… ({name})", flush=True)
+                emit(f"жду SSH {cfg.ssh_user}@{host}… ({name})")
             if (
                 is_auth
                 and auth_streak_started is not None
@@ -323,6 +330,10 @@ def run_script_sudo(
         _stream_pty_output(stdout, log=log, chunks=chunks)
         code = stdout.channel.recv_exit_status()
         err = stderr.read().decode("utf-8", errors="replace") if not stdout.channel.closed else ""
+        # PTY usually merges stderr; if anything remains, don't drop it past timed log.
+        if log and err.strip():
+            for line in err.strip().splitlines():
+                log(line)
         out = "".join(chunks)
         if code != 0:
             raise CloudError(f"remote script exit {code}: {err or out[-2000:]}")
@@ -354,6 +365,9 @@ def run_python(
         _stream_pty_output(stdout, log=log, chunks=chunks)
         code = stdout.channel.recv_exit_status()
         err = stderr.read().decode("utf-8", errors="replace") if not stdout.channel.closed else ""
+        if log and err.strip():
+            for line in err.strip().splitlines():
+                log(line)
         out = "".join(chunks)
         if code != 0:
             raise CloudError(f"remote python exit {code}: {err or out[-2000:]}")