refactor(examples): standardize example file structure

[cpcloud]

Summary

• normalize the file-level description banners across the 25 runnable examples in cuda_core/examples and cuda_bindings/examples
• standardize direct execution structure by using main() and if __name__ == "__main__" consistently, including moving the remaining cuda_core module-level execution into main()
• preserve the pytest-driven cuda_bindings example layout while adding the missing direct-execution guard for conjugateGradientMultiBlockCG_test.py

Follow Ups

• decide whether the normalized top-of-file description blocks should become module docstrings instead of comment banners
• handle the remaining example-polish follow-up items separately, including naming conventions, cleanup patterns, import/dependency policy, error/output consistency, and documentation coverage

Closes #1674

Made with Cursor

[rwgk]

Drive-by action: I just triggered a rerun of a failed Windows build (infrastructure flake). Hope that's helpful.

[cpcloud]

Yup, thanks!

[rwgk]

I looked at the changes pretty carefully: apart from the loss of the very useful comment block in cuda_core/examples/gl_interop_plasma.py it looks great to me.

[rwgk]

Approving so you can merge this in your morning; please see #1770 (comment)

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