VoxelBlockGrid update

[theNded]

• Provide Reset to address #4759
• Provide Prune to recycle outlier blocks
• Minor parameter adjustment for loading to avoid stdgpu hashmap overflow

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This change is 

[update-docs[bot]]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[yxlao]

LGTM after fixing unit tests.

[theNded]

Unit tests failed on CPU with ISPC turned on. Reason: when converting the bool result of element-wise boolean operations (eq, le, gt, etc) to scalars, True becomes 255 or equivalent while the expected result should be 1. It does not happen to conversions from created bool tensors to scalar tensors. Awaiting fix before merging.

[yxlao]

python -c "import open3d as o3d; print(o3d.core.Tensor.ones((3), o3d.core.int32).le(1).to(o3d.core.int32))"

When computing Tensor::Le() with ISPC, ISPC assigns 0b11111111 (255) for the true values. If we initialize a fresh tensor, the true value will always be 0b00000001.

Some discussions: https://stackoverflow.com/questions/51927616/c-bool-to-int-conversion-bug

[reyanshsolis]

If we initialize a fresh tensor, the true value will always be 0b00000001.

Is this even the case when using ISPC for initializing a new tensor?

[ssheorey]

Hi @theNded , do you have an update on this PR?

[theNded]

Let me close it for now and reopen after some upgrades.