refactor: iwyu

[Becheler]

Before submitting

• This PR targets the develop branch.
• I searched for an existing PR or issue covering the same change.
• My contribution is licensed under the Boost Software License 1.0.

Type of change

• Bug fix
• New feature or API addition
• Refactor (no behavior change)
• Documentation
• Build, CI, or tooling
• Other (specify below)

Does this PR introduce a breaking change?

• Yes (describe migration impact below)
• No

What this PR does

IWYU on two headers

Motivation

Testing

Checklist

• Existing tests pass (b2 in the test/ directory).
• New behavior is covered by a test, or this is a docs / build / refactor change.
• Documentation was updated if user-facing behavior changed.
• No new compiler warnings on the platforms I built against.

[github-actions]

Boost dependency footprint vs develop (auto-generated).
PR run 34055247619 vs develop run 34051347393 (6e892f02cb).

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

Dependency	develop	PR	Δ
parameter	3	2	-1

Transitive Boost modules: 47 → 47 (0)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 34055247558 vs develop run 34051347454 (6e892f02cb).

Job	Baseline	After	Delta
macos (clang, 14)	444	444	0
macos (clang, 17)	407	407	0
macos (clang, 20)	407	407	0
ubuntu (clang-19, 14)	444	444	0
ubuntu (clang-19, 17)	407	407	0
ubuntu (clang-19, 20)	407	407	0
ubuntu (clang-19, 23)	407	407	0
ubuntu (gcc-14, 14)	373	373	0
ubuntu (gcc-14, 17)	369	369	0
ubuntu (gcc-14, 20)	369	369	0
ubuntu (gcc-14, 23)	369	369	0
windows_msvc_14_3 (msvc-14.3)	961	961	0