CLIUtils/CLI11: v2.6.2

This version adds C++20 modules support, additional controls for help output and finer grained control for extras handling and prefix command operation. Fixes compatibility issues with C++26 and Windows and a number of small issue with help output and specific combinations of options and conditions. Added Added C++20 modules support with new module files and tests. #1286 Added configuration modes for extras handling: AssumeMultipleArguments and AssumeSingleArgument. #1270 Added option for full install including impl headers with precompiled option. #1252 Added improvements to prefix commands including PrefixCommandMode and separator specification. #1266 Added controls for option name formatting in help output, allowing disabling of default values, flags, and type names. #1247 Added refactor of Meson build system with updated version and new options. #1280 Added support for Bazel 9. #1287 Added module testing infrastructure. #1255 Changed Changed default to install impl headers even when precompiled option is selected. #1291 Updated copyright dates to 2026. #1283 Updated CI pipelines including Azure Pipelines and GitHub workflows. #1267, #1283 Updated documentation and book chapters. #1250 Fixed Fixed extra spaces in option and app descriptions. #1295 Fixed option searching to use fallthrough in parent apps. #1292 Fixed C++26 template ambiguity for std::complex. #1278 Fixed UTF-8 config filenames not supported on Windows. #1273 Fixed enumeration stream output generating unconvertible strings if certain a user supplied stream conversion method was supplied #1261 Fixed code simplification issues by removing use of static std::string which was causing some heap allocation issues when using CLI11 as part of DLL on certain operating systems #1244 Fixed MISRACPP2023-25_5_2-a-1 rule violation #1299