Fix Windows clang++ CI failure in maxpos sample by guarding CRT deprecation warnings

[Copilot]

The Use clang++ on windows-2022 job failed during the compile sweep because docs/examples/maxpos/sol-correct.cpp uses scanf, which is treated as deprecated under MSVC CRT and escalated by -Werror. This change removes that toolchain-specific failure without changing runtime behavior.

• Root cause

  • Windows clang++ (MSVC CRT) emits deprecated-CRT warnings for scanf in sol-correct.cpp; CI compiles with warnings-as-errors.

• Change

  • Added an MSVC-only preprocessor guard in docs/examples/maxpos/sol-correct.cpp:
    • defines _CRT_SECURE_NO_WARNINGS before including <cstdio>
  • Scope is intentionally local to the sample file that failed.

• Behavioral impact

  • No logic/path/output changes.
  • Only affects compile-time warning policy on MSVC-based toolchains.

#if defined(_MSC_VER)
#define _CRT_SECURE_NO_WARNINGS
#endif

#include <cstdio>