[hawick] Support passing std::reference_wrapper to boost::hawick_circuits

[ldionne]

Reported as ldionne/hawick_circuits#1.

[ldionne]

This supersedes #249 which I can't modify anymore for some reason.

[cppalliance-bot]

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2026-07-21 12:17:20 UTC

[ldionne]

@Becheler I created this PR from my own fork, so you can clean up any branches on the boostorg repo if desired.

[github-actions]

Boost dependency footprint vs develop (auto-generated).
PR run 29829351974 vs develop run 29738450065 (81ac21073b).

Header-inclusion weights (graph files pulling each direct dependency in):

No header-inclusion-weight changes.

Transitive Boost modules: 68 → 68 (0)

[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 29829351972 vs develop run 29738450095 (81ac21073b).

Job	Baseline	After	Delta
macos (clang, 14)	4	4	0
macos (clang, 17)	4	4	0
macos (clang, 20)	4	4	0
ubuntu (clang-19, 14)	4	4	0
ubuntu (clang-19, 17)	4	4	0
ubuntu (clang-19, 20)	4	4	0
ubuntu (clang-19, 23)	4	4	0
ubuntu (gcc-14, 14)	10	10	0
ubuntu (gcc-14, 17)	10	10	0
ubuntu (gcc-14, 20)	10	10	0
ubuntu (gcc-14, 23)	10	10	0
windows_msvc_14_3 (msvc-14.3)	971	971	0

[Becheler]

Other than just an obsolete guard, I think this is good to go ?
Thank you so much for your reactivity Louis ! 🙏🏽
Good to finally interact after seing your name everywhere ahahaha ❤️

[jeremy-murphy]

Other than just an obsolete guard, I think this is good to go ?
Thank you so much for your reactivity Louis ! 🙏🏽
Good to finally interact after seing your name everywhere ahahaha ❤️

Thanks for refreshing your PR, @ldionne. The only other modernization I would make right now is to use = delete on that copy constructor instead of making it private. Everything else I think we can do in a batch one day.

[ldionne]

Comments applied, thanks for the review and for the kind words!