[TomaSusi]

Adds a section on convergent-beam electron diffraction to the Bloch-wave tutorial (docs/user_guide/tutorials/blochwave.ipynb), for BlochWaves.calculate_cbed_patterns from abTEM#254.

The section comes before "Comparison to multislice". It explains how the probe's plane waves are solved and placed on its grid, why the extent should be a whole number of unit cells, and what the cost scales with. It then shows:

• a position-averaged (PACBED) thickness series of a 9 mrad probe on Si [001] at 200 keV, 100–500 Å;
• coherent patterns with a scan, with the probe on an atomic column and between columns, next to the PACBED pattern, where the overlapping {220} discs interfere;
• a paragraph on probe ensembles (defocus and aperture series share the Bloch-wave solutions; tilt series such as precession, and energies, are solved separately) and rotated crystals.

Only the new cells were executed, against abTEM#254's head (418d9442), and their outputs are committed; the rest of the notebook is unchanged apart from renumbered execution counts. The example uses g_max=4 and sg_max=0.1 and a 5 × 5 cell window, so the new cells run in about 15 s.

Merge after abTEM#254: the dev docs would otherwise describe a method that dev does not yet have.

🤖 Posted by Claude Code on behalf of Toma