Examples: Standardize file structure conventions

[rparolin]

Parent issue: #1673

Goal

Decide on and apply a consistent file structure pattern across all examples in both cuda_core/examples/ and cuda_bindings/examples/.

Current state

• Only 4 of 11 cuda.core examples use an if __name__ == "__main__" guard (show_device_properties.py, jit_lto_fractal.py, strided_memory_view_gpu.py, strided_memory_view_cpu.py).
• The other 7 run all code at module level with no function wrapping.
• Description blocks vary between single-line ("This demo illustrates how to...") and multi-line numbered bullet lists.
• Some files include ## Usage: sections with pip/python commands, others don't.

Decisions needed

1. Should all examples use if __name__ == "__main__"?
2. Should code be wrapped in a main() function or similar?
3. What format should the file-level description block follow?
4. Should usage instructions be included in every file?

Files affected

All 25 example files listed in #1673.