Replace the deprecated std::random_shuffle with std::shuffle

[Becheler]

clears -Wdeprecated-declarations on both clang and gcc : refer #496

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

Replace the deprecated std::random_shuffle (removed in C++17) with std::shuffle (avaiable in C++14)

• isomorphism.cpp and vf2_sub_graph_iso_test.cpp: dropped the BOOST_NO_CXX98_RANDOM_SHUFFLE guard, now always std::shuffle(..., gen), and removed the now-unused rand_fun.
• fibonacci_heap.cpp: same guard collapse to std::shuffle(..., gen).

Motivation

Refs #496

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]

Compiler-warning counts vs develop (auto-generated).
PR run 27952604737 vs develop run 27866501982 (29be624016).

Job	Baseline	After	Delta
macos (clang, 14)	46	41	-5
macos (clang, 17)	41	41	0
macos (clang, 20)	41	41	0
ubuntu (clang-19, 14)	46	41	-5
ubuntu (clang-19, 17)	46	41	-5
ubuntu (clang-19, 20)	46	41	-5
ubuntu (clang-19, 23)	46	41	-5
ubuntu (gcc-14, 14)	28	23	-5
ubuntu (gcc-14, 17)	28	23	-5
ubuntu (gcc-14, 20)	28	23	-5
ubuntu (gcc-14, 23)	28	23	-5
windows_msvc_14_3 (msvc-14.3)	974	974	0