Add CPM local cache support

Author: haohaolee

.gitignore

@@ -24,15 +24,16 @@ Makefile
 
 # CPM cache (optional - can be shared across projects)
 _deps/
+.cpm-cache/
 
 # IDE and editor files
 .idea/
 .vscode/
 .vs/
 .devcontainer/
 compile_commands.json
-DartConfiguration.tcl
-**/*.cbp
+.clangd/
+.cache/
 tags
 
 # macOS

CMakeLists.txt

@@ -3,6 +3,12 @@ project(developer_joyofenergy_cpp)
 
 set(CMAKE_CXX_STANDARD 17)
 
+# Set CPM cache directory to avoid re-downloading dependencies
+# Can be overridden by environment variable CPM_SOURCE_CACHE
+if(NOT CPM_SOURCE_CACHE)
+    set(CPM_SOURCE_CACHE "${CMAKE_SOURCE_DIR}/.cpm-cache" CACHE PATH "CPM cache directory")
+endif()
+
 # Include CPM package manager
 include(cmake/CPM.cmake)