Migrate to C++20 and drop CUDA 11 support

[Empyreus]

This PR bumps the project's C++ language standard from C++17 to C++20 (host, CUDA, and HIP) and removes support for CUDA 11, which cannot compile C++20. CI matrices are updated to drop CUDA 11.8 and add CUDA 13.0 alongside 12.9.

• C++20 enables newer language features across the codebase.
• C++20 requires CUDA ≥ 12.0, so CUDA 11.8 can no longer be supported.
• Blackwell / sm_100 targets require CUDA ≥ 12.8, so CUDA 13.x is added to CI coverage.

[Empyreus]

/azp run

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Azure Pipelines successfully started running 6 pipeline(s).

[Empyreus]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).

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[Binyang2014]

LGTM