class_docstr: FCOS ARSL network, see https://arxiv.org/abs/
  
  Args:
      backbone (object): backbone instance
      neck (object): 'FPN' instance
      fcos_head (object): 'FCOSHead_ARSL' instance
      fcos_cr_loss (object): 'FCOSLossCR' instance, only used for semi-det(ssod) by ARSL
code: def model_forward(self):
      body_feats = self.backbone(self.inputs)
      fpn_feats = self.neck(body_feats)
      fcos_head_outs = self.fcos_head(fpn_feats)
      return fcos_head_outs
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import paddle
  from ppdet.core.workspace import register, create
  from .meta_arch import BaseArch
label_desc: Use image node_id 4 for calling the ARSL_FCOS obj's underlying member method code with example usage: obj.model_forward() and returns: fcos_head_outs