Fix/dependency updates

[kamildrejer]

The fix contains:

• Bump onnxruntime lower bound to >=1.23.0 (required for opset 21/22/23 support)
• Bump opencv-python-headless lower bound to >=4.10.0
• Remove upper version caps that prevented installation of current releases
• Fix sys.path.append -> sys.path.insert(0,...) so plugin env takes priority
  over OSGeo4W system-installed onnxruntime
• Fix IndexError in detector.py: get_outputs_channel_names() can return None
  or empty list; accessing [0] directly caused 'list index out of range' when
  loading models without class_names metadata"