[WIP] Lidarseg

[sunjiahao1999]

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Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the back-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (0ef13b8) 47.26% compared to head (4ba030a) 47.28%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
mmdet3d/datasets/seg3d_dataset.py	0.00%	4 Missing ⚠️
mmdet3d/models/backbones/spvcnn_backone.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## main #2909 +/- ## ========================================== + Coverage 47.26% 47.28% +0.01%  ========================================== Files 277 277 Lines 23415 23429 +14 Branches 3655 3658 +3 ========================================== + Hits 11067 11078 +11  - Misses 11635 11638 +3  Partials 713 713 

Flag	Coverage Δ
unittests	47.28% <72.22%> (+0.01%)	⬆️

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