Add PEP 723 dependency metadata to examples

[shrishsk]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md.
• [ ] I've added tests applicable for this pull request

What does this Pull Request accomplish?

Adds PEP 723 dependency metadata after the module docstring in all 53 Python examples. Each script declares its directly imported third-party packages, including numpy, nitypes, matplotlib, and nptdms where applicable.

Closes #1030.

Why should this Pull Request be merged?

PEP 723-aware script runners can use the metadata to install the dependencies needed by each example, making the examples easier to run. Keeping the docstring first makes each example’s purpose immediately visible.

What testing has been done?

• Audited imports in all 53 scripts against their declared distributions; all matched.
• uv export --script parsed and resolved dependencies for all 53 scripts.
• Ran pipx run --path on four examples importing matplotlib or nptdms. Dependency installation succeeded, but execution stopped at DAQmx calls because NI-DAQmx is not installed in the test environment.
• git diff --check passed.

[zhindes]

Let's make sure @bkeryan reviews as well :)

[shrishsk]

@bkeryan Thanks for the feedback. I moved the metadata below each docstring, updated the changelog, and revised the PR description to follow the project template and accurately reflect validation.

[shrishsk]

@bkeryan Thanks for the suggestion. I added the pipx/uv usage paragraph to the README’s Python Examples section and updated the changelog wording to explain how users can run examples with their dependencies installed automatically.