Daily Backlog Burner: Add include directory for easier Z3 integration (#7907)

This change addresses issue #1664 by implementing an include directory that
consolidates all Z3 API headers in one convenient location for developers.

## Implementation

- Creates `build/include/` directory during CMake configuration
- Copies all Z3 API headers (z3*.h) and C++ API header (z3++.h) to include directory
- Updates libz3 target to expose the include directory via target_include_directories
- Uses CMake custom target with POST_BUILD commands for automatic header copying

## Benefits

- **Developer Experience**: Single include directory eliminates need to specify multiple paths
- **Build Integration**: Works seamlessly with existing CMake build system
- **API Completeness**: Includes both C API and C++ API headers
- **Automatic Updates**: Headers are copied automatically during build process

## Usage

Developers can now:
- Use `-I build/include` for manual compilation
- Benefit from automatic include path setup when using Z3 via CMake find_package()
- Access all Z3 API headers from a single, predictable location

This follows the standard C/C++ project convention of having a dedicated include
directory, making Z3 easier to integrate into external projects.

Closes #1664

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Daily Backlog Burner <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

src/CMakeLists.txt

@@ -167,6 +167,60 @@ endif()
 # so that if those are also shared libraries they are referenced by `libz3.so`.
 target_link_libraries(libz3 PRIVATE ${Z3_DEPENDENT_LIBS})
 
+################################################################################
+# Create include directory with headers for easier developer integration
+################################################################################
+set(Z3_BUILD_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include")
+file(MAKE_DIRECTORY "${Z3_BUILD_INCLUDE_DIR}")
+
+# Copy Z3 API headers to build include directory
+set(Z3_API_HEADERS
+  api/z3.h
+  api/z3_api.h
+  api/z3_algebraic.h
+  api/z3_ast_containers.h
+  api/z3_fixedpoint.h
+  api/z3_fpa.h
+  api/z3_logger.h
+  api/z3_macros.h
+  api/z3_optimization.h
+  api/z3_polynomial.h
+  api/z3_private.h
+  api/z3_rcf.h
+  api/z3_replayer.h
+  api/z3_spacer.h
+  api/z3_v1.h
+  api/c++/z3++.h
+)
+
+# Create custom target to copy headers
+add_custom_target(z3_headers_copy ALL
+  COMMENT "Copying Z3 API headers to build include directory"
+)
+
+foreach(header_file ${Z3_API_HEADERS})
+  get_filename_component(header_name "${header_file}" NAME)
+  set(src_file "${CMAKE_CURRENT_SOURCE_DIR}/${header_file}")
+  set(dst_file "${Z3_BUILD_INCLUDE_DIR}/${header_name}")
+
+  add_custom_command(
+    TARGET z3_headers_copy POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            "${src_file}"
+            "${dst_file}"
+    COMMENT "Copying ${header_name} to include directory"
+    VERBATIM
+  )
+endforeach()
+
+# Make libz3 depend on header copying
+add_dependencies(libz3 z3_headers_copy)
+
+# Update libz3 to also expose the build include directory
+target_include_directories(libz3 INTERFACE
+  $<BUILD_INTERFACE:${Z3_BUILD_INCLUDE_DIR}>
+)
+
 # This is currently only for the OpenMP flags. It needs to be set
 # via `target_link_libraries()` rather than `z3_append_linker_flag_list_to_target()`
 # because when building the `libz3` as a static library when the target is exported