callback improvements

[casperdcl]

• [ ] rebase after #1913 is merged
  • [x] fixes #1913 interval logic ported from SyneRBI/PETRIC:petric.py
• [x] fixes https://github.com/TomographicImaging/CIL/pull/1892#pullrequestreview-2277630302 naming
• [ ] check Hackathon-000-Stochastic-QualityMetrics:img_quality_cil_stir/image_quality_callback.py
• [ ] check SyneRBI/PETRIC:petric.py
• [ ] check https://keras.io/api/callbacks/
  • [ ] see also #420
• [ ] potentially move some of above to epic issue