Separate `motools.experiments` dependencies into separate group?

[dtch1997]

Supports the usage of motools without the peripheral experiment reproduction harness

[coderabbitai]

A summary of the changes CodeRabbit can apply:

• Split off motools.experiments into an optional dependency group and updated docs/code accordingly: modified pyproject.toml to add an experiments extras group (moved scipy, matplotlib, plotly, kaleido; left pandas in core), updated README.md with optional-install instructions, updated motools/experiments/init.py docstring to note optional dependencies and install command, and added docs/optional_dependencies.md as a comprehensive guide so the core package is lighter and experiments are opt-in.

• Add optional "experiments" feature: create docs/optional_dependencies.md documenting the experiments module and install options, add an experiments extras group to pyproject.toml (scipy, matplotlib, plotly, kaleido), update README.md to mention the optional experiments utilities, create .sed-tmp with a uv sync hint, and trim the motools/experiments/init.py module docstring.

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