fix: Resolve mypy [valid-type] error for TorchTensor TypeAlias

[Copilot]

What this PR does / why we need it:

Fixes mypy type checking error where TorchTensor was not recognized as a valid type alias:

feast/online_response.py:104: error: Variable "feast.online_response.TorchTensor" is not valid as a type [valid-type]

Root Cause

TypeAlias imported at module level while type alias defined conditionally inside TYPE_CHECKING block. Mypy cannot disambiguate whether TorchTensor is a variable or type alias.

Changes

Move TypeAlias import into both branches of TYPE_CHECKING conditional:

# Before
from typing import TYPE_CHECKING, Any, Dict, List, TypeAlias, Union
if TYPE_CHECKING:
    import torch
    TorchTensor: TypeAlias = torch.Tensor
else:
    TorchTensor: TypeAlias = Any

# After  
from typing import TYPE_CHECKING, Any, Dict, List, Union
if TYPE_CHECKING:
    from typing import TypeAlias
    import torch
    TorchTensor: TypeAlias = torch.Tensor
else:
    from typing import TypeAlias
    TorchTensor: TypeAlias = Any

Type-checking only change. No runtime impact.

Misc

N/A

Original prompt

---

This section details on the original issue you should resolve

<issue_title>torch tensor type error with mypy</issue_title>
<issue_description>## Expected Behavior

Current Behavior

feast/online_response.py:104: error: Variable "feast.online_response.TorchTensor" is not valid as a type [valid-type]

Steps to reproduce

Specifications

• Version:
• Platform:
• Subsystem:

Possible Solution

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes torch tensor type error with mypy #5563

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[jyejare]

LGTM, needs to rerun checks I think.