Operel/mvdataset docker qol

[orperel]

Quality of life improvements, these are all small local changes fit together:

• docker issue: bumpy spicy version to >=1.7.2 (user complaints on github)
• fix issue with validation splits missing in standard nerf (fix was in place and removed, restored here)
• ensure all dataset fields are declared in ctor
• basic decoder support for layer type ‘linear’ -> nn.Linear (previously was only called ‘none’ in config)
• offline renderer doesn’t assume matcap by default (which is specific to sdf pipelines right now)