[Feature] Add inferencer for LiDAR-based detection

[JingweiZhang12]

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Motivation

Inherit from the BaseInferencer in MMEngine

Modification

Compare with the MonoDet3D inferencer PR, there are some modifications:

1. Move _inputs_to_list to BaseDet3DInferencer.
2. inputs type here: dict[list] > list[dict]
3. unify some naming formats.
4. Add registry INFERENCERS

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.

[JingweiZhang12]

The UT and inference with an example input are OK.
TODO:

• docstrings need to be polished.
• LidarDet3DInferencer will inherit from BaseDet3DInferencer in the PR [Feature] add mono3d inferencer #2190 and remove some duplicated function. This modification will be done when PR2190 is merged.

[JingweiZhang12]

@gaotongxiao, please review this PR.

[gaotongxiao]

The issues overall are similar to #2190. You can revise your code according to the comments in that PR.

[codecov]

Codecov Report

Base: 46.12% // Head: 46.37% // Increases project coverage by +0.24% 🎉

Coverage data is based on head (516e538) compared to base (278df1e).
Patch coverage: 60.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #2208      +/-   ##
===========================================
+ Coverage    46.12%   46.37%   +0.24%     
===========================================
  Files          258      259       +1     
  Lines        21285    21390     +105     
  Branches      3365     3379      +14     
===========================================
+ Hits          9818     9919     +101     
  Misses       10827    10827              
- Partials       640      644       +4     

Flag	Coverage Δ
unittests	46.37% <60.00%> (+0.24%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet3d/datasets/transforms/__init__.py	100.00% <ø> (ø)
mmdet3d/datasets/transforms/loading.py	47.33% <41.66%> (-0.22%)	⬇️
mmdet3d/apis/inferencers/lidar_det3d_inferencer.py	57.57% <57.57%> (ø)
mmdet3d/apis/inferencers/base_det3d_inferencer.py	86.31% <73.33%> (-1.19%)	⬇️
mmdet3d/apis/__init__.py	100.00% <100.00%> (ø)
mmdet3d/apis/inferencers/__init__.py	100.00% <100.00%> (ø)
mmdet3d/apis/inferencers/mono_det3d_inferencer.py	89.83% <100.00%> (+4.98%)	⬆️
mmdet3d/registry.py	100.00% <100.00%> (ø)
mmdet3d/datasets/transforms/transforms_3d.py	33.33% <0.00%> (+0.11%)	⬆️
mmdet3d/structures/det3d_data_sample.py	98.41% <0.00%> (+0.16%)	⬆️
... and 3 more

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