Implement 3D connected component analysis

[dimitrivlachos]

This implements 3D connected components analysis into the
Fast FeedbackService, enabling the processing of rotation datasets
while maintaining real-time feedback.

Previously, connected components — spots — were processed per
image, treating each frame as independent 2D data. However, in rotation
datasets, spots extend across multiple images, forming 3D reflections
that require all collected frames to fully resolve. At the same time,
real-time feedback still depends on per-frame 2D calculations.

This update enables both:

• 2D connected components (2DCC) are computed per frame for real-time
  feedback.
• 2DCC results are stored and recombined at the end of a sweep for fast
  and efficient 3D analysis.

Changes:

• Extracted ConnectedComponents into separate files for improved
  modularity, readability and logical grouping.
• Refactored 2D connected components into an object-oriented structure.
• Introduced Signal and Reflection objects for data encapsulation.
• Implemented 3D connected components using precomputed 2D connectivity
  data.
• Added 3D filtering based on max_peak_centroid_separation and
  min_spot_size_3d
• Integrated dx2 for writing 3D connected components to a reflection
  table.

The dx2 integration relies on the pending h5_writer branch:
dials/dx2#2

[dimitrivlachos]

Other than a review, this is the only thing holding up the PR as I await dials/dx2#2 to be merged so I can tag it explicitly.