Prefer static operator() if available

[mingxwa]

Motivation

Static operator() is a C++23 feature that can improve code generation. Although won't help much in optimized builds, it's the recommended way to define an operator() function nowadays. Resolves #258.

Changes

• Updated implementation of the built-in dispatch types to use static operator() if available.
• Updated existing BVT to build proxy in C++23 mode with the latest compilers.
• Added bvt-compatibility.yml to build proxy in C++20 mode. -Wno-c++2b-extensions is required for Clang in C++20 mode to avoid warnings when building tests.
• Added a unit test case for multidimensional subscript (requires C++23).

[Copilot]

PR Overview

This PR updates the CI workflows to support building and testing the "proxy" component in C++23 mode, aligning with the new static operator() convention. Key changes include:

• Updating various workflow files to use C++23 by setting the CMAKE_CXX_STANDARD flag.
• Consolidating build directories for several CI jobs.
• Adding a new compatibility test workflow for C++20 mode with Clang.

Reviewed Changes

File	Description
.github/workflows/bvt-compatibility.yml	New workflow file for C++20 compatibility builds.
.github/workflows/bvt-appleclang.yml	Updated build command to enforce C++23.
.github/workflows/bvt-msvc.yml	Updated build command and runner version.
.github/workflows/bvt-clang.yml	Streamlined to use clang-19 with C++23.
.github/workflows/bvt-gcc.yml	Consolidated build directory and enforced C++23.
.github/workflows/bvt-nvhpc.yml	Consolidated build directory and enforced C++23.
.github/workflows/pipeline-ci.yml	Added a step to run the new compatibility workflow.

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.