Add configure_family_by_name helper

[LeonidElkin]

Summary

Add a public helper function configure_family_by_name(...) for configuring and registering a single built-in family by its name.

Currently, users often need to call the global family registration function even when they only need one family.

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Problem

The current workflow usually requires configuring the whole families register even for small examples that use only one family.

A focused helper would make examples, tests, and interactive usage simpler and more explicit.

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Proposed API

Add a helper function:

configure_family_by_name(name: str) -> None

Optionally, the function may return the configured family if this fits the existing API design.

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Expected behavior

The function should configure/register only the requested family.

If an unknown family name is passed, the function should raise a clear exception, for example KeyError or a project-specific exception if one already exists.

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Acceptance criteria

1. configure_family_by_name(name: str) is added to the public configuration API.
2. The helper registers/configures the requested built-in family.
3. Unknown family names produce a clear error.
4. The function is covered by tests.
5. At least one example or documentation page uses the new helper.