fix(asio): Fix asio dependency issue

[david-cermak]

Closes #1044

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Note

Low Risk
Changes are limited to header include gating and CI/test additions; primary risk is an unintended build regression if ASIO_SOURCE isn’t set where expected.

Overview
Fixes a downstream build break where including asio.hpp could require sock_utils headers. socketpair.h is now included only when building Asio’s own translation unit (ASIO_SOURCE), keeping sock_utils off consumers’ include paths.

Adds a new components/asio/tests/build_test build-only regression project (and wires it into the GitHub Actions matrix with version exclusions) to ensure a component that only declares REQUIRES asio can compile and link.

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