Before this change, downstream CMake consumers of libosrm had to copy
example/cmake/FindLibOSRM.cmake into their project and prepend it to
CMAKE_MODULE_PATH. That find-module was a hand-rolled pkg-config
wrapper that returned flag-string variables — no imported targets, no
transitive usage requirements, no auto-discovery.

Ship a proper CMake Config Package instead, matching the pattern used
by every modern C++ library we depend on via vcpkg (flatbuffers, fmt,
nlohmann_json, protozero, TBB). Consumers now only need:

  find_package(LibOSRM REQUIRED)
  target_link_libraries(myapp PRIVATE osrm::osrm)

No CMAKE_MODULE_PATH tweak, no pkg-config, no manual dependency
find_package() calls — LibOSRMConfig.cmake re-declares Boost, TBB,
Threads, and ZLIB via find_dependency() on behalf of the consumer.

Changes:
- New cmake/LibOSRMConfig.cmake.in template consumed by
  configure_package_config_file(); paired with
  write_basic_package_version_file(VERSION OSRM_VERSION
  COMPATIBILITY SameMinorVersion) for version-range checks.
- install(TARGETS osrm ... EXPORT LibOSRMTargets ...) +
  install(EXPORT LibOSRMTargets NAMESPACE osrm::) writes
  lib/cmake/LibOSRM/LibOSRMTargets.cmake with the imported target
  definition, IMPORTED_LOCATION, INTERFACE_INCLUDE_DIRECTORIES, and
  INTERFACE_LINK_LIBRARIES baked in.
- target_include_directories(osrm INTERFACE ...) exposes the public
  include dir via BUILD_INTERFACE (subproject builds) and two
  INSTALL_INTERFACE entries — both include and include/osrm — so
  consumer code using either #include <osrm/...> or the internal
  "engine/api/..." non-prefixed paths resolves after install.
- ZLIB_LIBRARY and CMAKE_THREAD_LIBS_INIT uses replaced with their
  imported-target equivalents (ZLIB::ZLIB, Threads::Threads) so
  ENGINE_LIBRARIES serialises cleanly into LibOSRMTargets.cmake
  instead of absolute file paths that would be non-portable across
  install prefixes.

Scope: only osrm (the routing engine) is exposed as a Config Package
target. The other six osrm_* libraries are build-internal support for
the command-line tools and keep their existing plain install(TARGETS
... DESTINATION lib) rules; exposing them as imported targets would
require modernising the OSMIUM_LIBRARIES / EXPAT / BZIP2 / LUA
variables to imported targets, which is left for a follow-up. This
matches the scope of the removed find-module, which only ever covered
the routing library.

libosrm.pc is kept as-is for Make/Meson/autotools consumers that have
no CMake. example/cmake/FindLibOSRM.cmake is deleted — superseded by
LibOSRMConfig.cmake. example/CMakeLists.txt is rewritten from the
variable-splicing dance down to find_package + target_link_libraries.

Verified end-to-end:
- cmake --install to a scratch prefix produces the expected four
  files under lib/cmake/LibOSRM/ (Config, ConfigVersion, Targets,
  Targets-release).
- A fresh consumer project (stripped copy of example/) with only
  CMAKE_PREFIX_PATH pointed at the scratch prefix configures,
  compiles, and links osrm-example against osrm::osrm without any
  other hints.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>