fix observation vector issue #324 - #325

Description

This PR fixes an issue where vectorized environments returned identical observations across all environments by explicitly specifying NumPy strides when constructing arrays from EnvPool buffers.

• In envpool/core/py_envpool.h, replaced the default py::array constructor with one that passes a computed strides vector based on a.Shape() and sizeof(dtype).
• This ensures the Python view matches the actual memory layout of the underlying buffer and preserves zero-copy behavior.
• Added an inline comment explaining the stride calculation and rationale.

Key change:

• From: py::array(a.Shape(), reinterpret_cast<dtype*>(a.Data()), capsule)
• To: py::array(py::dtype::of(), a.Shape(), strides, reinterpret_cast<dtype*>(a.Data()), capsule)

Motivation and Context

close #324

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

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• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• New environment (non-breaking change which adds 3rd-party environment)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of example)

Implemented Tasks

• Pass explicit strides in py_envpool.h NumPy array construction

Checklist

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• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
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