Fast rebuilds of C/C++ code when needed. (#106)

* Fast rebuilds of C/C++ code when needed. Configures 
* `CMake` to use `ccache` for faster C/C++ compilation.
* Modifies `pyproject.toml` to enable `editable.rebuild` and specify `build-dir` for `scikit-build-core`, ensuring fast, incremental rebuilds when C/C++ sources or project metadata change.

Author: jbcoe

CMakeLists.txt

@@ -12,6 +12,18 @@ endif()
 string(REGEX MATCH "^[0-9]+(\\.[0-9]+)*" CMAKE_NLE_VERSION "${NLE_VERSION}")
 project(nle VERSION ${CMAKE_NLE_VERSION})
 
+# Only enable ccache if this is the main project, not a sub-dependency.
+if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
+  find_program(CCACHE_EXECUTABLE ccache)
+  if(CCACHE_EXECUTABLE)
+    message(STATUS "ccache found, enabling for C and C++")
+    set(CMAKE_C_COMPILER_LAUNCHER "${CCACHE_EXECUTABLE}")
+    set(CMAKE_CXX_COMPILER_LAUNCHER "${CCACHE_EXECUTABLE}")
+  else()
+    message(STATUS "ccache not found, proceeding without it")
+  endif()
+endif()
+
 if(CMAKE_BUILD_TYPE MATCHES Debug)
   message("Debug build.")
   # Unclear if this is even necessary. `dsymutil rlmain -o rlmain.dSYM` seems to

pyproject.toml

@@ -38,6 +38,8 @@ cmake.build-type = "Release"
 cmake.args = ["-DHACKDIR=nle/nethackdir", "-DPYTHON_PACKAGE_NAME=nle"]
 minimum-version = "build-system.requires"
 metadata.version.provider = "scikit_build_core.metadata.setuptools_scm"
+build-dir = "build/{wheel_tag}"
+editable.rebuild = true
 generate = [
   { path = "nle/version.py", template = '__version__ = "${version}"' },
 ]