Update the vendored BESA CMake module

A generated C++ project contains a project-owned copy of BESA under cmake/besa. Update only that copy with:

besa cpp update --project .

To use another relative location:

besa cpp update --project . --module-path bs/besa

--module-path is always relative to the project root. BESA refuses absolute paths and paths which escape the project with ...

Updates replace the BESA-owned directory as a unit. BESA checks for its management marker before replacing an existing directory, so a mistyped module path cannot silently delete an unrelated project directory. The command never parses or edits project-owned CMakeLists.txt files.