Example CMakeLists duplicated the same dependency discovery and link
setup. Move that into brpc_example_find_common_deps in
BrpcExample.cmake, migrate MySQL and other examples to use it, and
implement the helper as a macro so CMAKE_PREFIX_PATH, include paths,
and DYNAMIC_LIB propagate to the caller scope.
Example-specific deps stay local (e.g. readline/ncurses/thriftnb for
MySQL, gperftools for redis/http). LINK_SO behavior is unchanged.
* build(cmake): keep modern CMake policy compatibility
Raise the minimum CMake version range to 3.16...3.28 so CMake 4.x no longer treats the project as relying on removed pre-3.5 policy compatibility. The range preserves a conservative 3.16 runtime floor while documenting policy validation through 3.28.
* build(cmake): modernize target-scoped CMake configuration
Move shared compile definitions, include paths, options, and link dependencies onto interface targets so top-level, src, tools, tests, and standalone examples consume consistent build settings without relying on global directory state.
Examples now share a small CMake helper, and the gtest download path is updated to configure with modern CMake while keeping downloaded gtest headers ahead of Homebrew's C++17-only installation.
Bright Chen