Enhance training and logging functionality with accelerator support

- Added support for multi-GPU training by introducing an `accelerator` parameter in training functions.
- Updated `update_policy` to handle gradient updates based on the presence of an accelerator.
- Modified logging to prevent duplicate messages in non-main processes.
- Enhanced `set_seed` and `get_safe_torch_device` functions to accommodate accelerator usage.
- Updated `MetricsTracker` to account for the number of processes when calculating metrics.
- Introduced a new feature in `pyproject.toml` for the `accelerate` library dependency.

src/lerobot/utils/utils.py

@@ -20,6 +20,7 @@ import select
 import subprocess
 import sys
 import time
+from collections.abc import Callable
 from copy import copy, deepcopy
 from datetime import datetime
 from pathlib import Path
@@ -49,13 +50,15 @@ def auto_select_torch_device() -> torch.device:
 
 
 # TODO(Steven): Remove log. log shouldn't be an argument, this should be handled by the logger level
-def get_safe_torch_device(try_device: str, log: bool = False) -> torch.device:
+def get_safe_torch_device(
+    try_device: str, log: bool = False, accelerator: Callable | None = None
+) -> torch.device:
     """Given a string, return a torch.device with checks on whether the device is available."""
     try_device = str(try_device)
     match try_device:
         case "cuda":
             assert torch.cuda.is_available()
-            device = torch.device("cuda")
+            device = accelerator.device if accelerator else torch.device("cuda")
         case "mps":
             assert torch.backends.mps.is_available()
             device = torch.device("mps")
@@ -109,6 +112,7 @@ def init_logging(
     display_pid: bool = False,
     console_level: str = "INFO",
     file_level: str = "DEBUG",
+    accelerator: Callable | None = None,
 ):
     def custom_format(record: logging.LogRecord) -> str:
         dt = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
@@ -137,6 +141,10 @@ def init_logging(
     console_handler.setFormatter(formatter)
     console_handler.setLevel(console_level.upper())
     logger.addHandler(console_handler)
+    if accelerator is not None and not accelerator.is_main_process:
+        # Disable duplicate logging on non-main processes
+        logging.info(f"Setting logging level on non-main process {accelerator.process_index} to WARNING.")
+        logging.getLogger().setLevel(logging.WARNING)
 
     # Additionally write logs to file
     if log_file is not None:
@@ -158,6 +166,10 @@ def format_big_number(num, precision=0):
     return num
 
 
+def is_launched_with_accelerate() -> bool:
+    return "ACCELERATE_MIXED_PRECISION" in os.environ
+
+
 def say(text: str, blocking: bool = False):
     system = platform.system()