Replace deprecated 'pretrained' with 'init_cfg' in NuImages configs

[dhruvildarji]

Summary

• Replace the deprecated model-level pretrained argument with init_cfg inside the backbone dict across all NuImages configs and base model configs
• In mmdet v3.x, the pretrained parameter was removed from detector constructors (e.g., MaskRCNN, CascadeRCNN, HybridTaskCascade) in favor of backbone.init_cfg
• This fixes the TypeError: MaskRCNN.__init__() got an unexpected keyword argument 'pretrained' when running NuImages inference/testing

Affected Files

Base model configs:

• configs/_base_/models/mask-rcnn_r50_fpn.py
• configs/_base_/models/cascade-mask-rcnn_r50_fpn.py

NuImages configs (9 files):

• mask-rcnn_r101_fpn_1x_nuim.py
• mask-rcnn_x101_32x4d_fpn_1x_nuim.py
• mask-rcnn_r50_caffe_fpn_1x_nuim.py
• mask-rcnn_r50_caffe_fpn_coco-3x_1x_nuim.py
• mask-rcnn_r50_caffe_fpn_coco-3x_20e_nuim.py
• cascade-mask-rcnn_r101_fpn_1x_nuim.py
• cascade-mask-rcnn_x101_32x4d_fpn_1x_nuim.py
• htc_r50_fpn_head-without-semantic_1x_nuim.py
• htc_x101_64x4d_fpn_dconv_c3-c5_coco-20e-1xb16_nuim.py

Migration Pattern

Before:

model = dict(
    type='MaskRCNN',
    pretrained='torchvision://resnet50',
    backbone=dict(type='ResNet', ...),
    ...)

After:

model = dict(
    type='MaskRCNN',
    backbone=dict(
        type='ResNet', ...,
        init_cfg=dict(type='Pretrained', checkpoint='torchvision://resnet50')),
    ...)

Fixes #3136

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[dhruvildarji]

I just signed it. Thanks