Modernizes type hints in ignite/metrics/accumulation.py to use Python 3.10+ union syntax per issue #3481.

Changes

• Union[A, B] → A | B (11 instances)
• Tuple[...] → tuple[...] (1 instance)
• Removed unused Union, Tuple imports

Example

# Before
def __init__(
    self,
    device: Union[str, torch.device] = torch.device("cpu"),
) -> None:
    ...

def compute(self) -> Union[float, torch.Tensor]:
    ...

# After  
def __init__(
    self,
    device: str | torch.device = torch.device("cpu"),
) -> None:
    ...

def compute(self) -> float | torch.Tensor:
    ...

Affects VariableAccumulation, Average, and GeometricAverage classes.

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