fix: bound sequential_vertex_coloring

[Becheler]

#627

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

Bounds the main loop of the three argument sequential_vertex_coloring by the number of vertices in vertices(g) instead of num_vertices(g).

Motivation

filtered_graph reports the underlying count from num_vertices() while vertices() yields only the kept vertices. The order built from vertices(g) is therefore shorter, and the loop read past its end, then passed a garbage descriptor to adjacent_vertices().

Testing

Two filtered graph tests added:

1. feed the three argument overload an order map that counts out of range queries,
   so the old code fails deterministically on every compiler with no undefined behavior.
2. cover the reporter's two argument call. Filtered out vertices must keep a sentinel.

Docs updated for the [0, n) range.

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 37599415826 vs develop run 37447552382 (583c900edb).

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

No header-inclusion-weight changes.

Transitive Boost modules: 47 → 47 (0)

[cppalliance-bot]

An automated preview of the documentation is available at https://630.graph.prtest3.cppalliance.org/libs/graph/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-10-07 09:19:33 UTC

[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 37599415683 vs develop run 37447552015 (583c900edb).

Job	Baseline	After	Delta
macos (clang, 14)	392	392	0
macos (clang, 17)	391	391	0
macos (clang, 20)	391	391	0
ubuntu (clang-19, 14)	392	392	0
ubuntu (clang-19, 17)	391	391	0
ubuntu (clang-19, 20)	391	391	0
ubuntu (clang-19, 23)	391	391	0
ubuntu (gcc-14, 14)	345	345	0
ubuntu (gcc-14, 17)	341	341	0
ubuntu (gcc-14, 20)	341	341	0
ubuntu (gcc-14, 23)	341	341	0
windows_msvc_14_3 (msvc-14.3)	931	931	0

[codecov]

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