This commit adds two new Go programs to the `examples` directory to
demonstrate how to use the `pkg/matrix` and `pkg/datanode` packages
programmatically:
- `examples/create_matrix_programmatically`: Shows how to create a
`.matrix` file from scratch.
- `examples/run_matrix_programmatically`: Shows how to unpack and execute
a `.matrix` file using `runc`.
The `examples` directory has been reorganized to place each runnable
example in its own subdirectory, which is the standard Go practice for
handling multiple `main` packages.
