build: fix gemmi-config.cmake and change defaults in pyproject.toml

gemmi-config.cmake didn't work if ZLIB was not found

and two unrelated changes:

in CMakeLists.txt, python module is marked as COMPONENT py,
so that it's possible to install only python module with:
cmake --install <dir> --component py

in pyproject.toml, setting BUILD_GEMMI_PROGRAM and INSTALL_DEV_FILES
to OFF was removed, so it's ON by default.
But it's set to off in cibuildwheel configuration.

CMakeLists.txt

@@ -161,7 +161,7 @@ else()
   endif()
   set_property(TARGET ungz PROPERTY POSITION_INDEPENDENT_CODE ON)
   macro(support_gz exe)
-    target_sources(${exe} PUBLIC $<TARGET_OBJECTS:ungz>)
+    target_sources(${exe} PRIVATE $<TARGET_OBJECTS:ungz>)
   endmacro()
 endif()
 
@@ -473,5 +473,5 @@ if (USE_PYTHON)
   # Using Python_SITEARCH/SITELIB is not good, because they are absolute
   # and don't respect CMAKE_INSTALL_PREFIX.
   # https://discourse.cmake.org/t/findpython3-how-to-specify-local-installation-directory-for-python-module/3580/5
-  install(TARGETS gemmi_py DESTINATION "${Python_SITEARCH}")
+  install(TARGETS gemmi_py DESTINATION "${Python_SITEARCH}" COMPONENT py)
 endif()

pyproject.toml

@@ -64,8 +64,6 @@ cmake.build-type = "Release"
 cmake.verbose = true
 [tool.scikit-build.cmake.define]
 USE_PYTHON = "ON"
-BUILD_GEMMI_PROGRAM = "OFF"
-INSTALL_DEV_FILES = "OFF"
 
 [tool.scikit-build.metadata.version]
 provider = "scikit_build_core.metadata.regex"

tools/gemmi-config.cmake.in

@@ -1,7 +1,7 @@
 @PACKAGE_INIT@
 
 include(CMakeFindDependencyMacro)
-find_dependency(ZLIB)
+find_package(ZLIB)
 
 include("${CMAKE_CURRENT_LIST_DIR}/gemmi-targets.cmake")