Add sandbox_c cmake project + ccache workflow for pool testing

sandbox_c/CMakeLists.txt

@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.22)
+project(sandbox_c C)
+set(CMAKE_C_STANDARD 11)
+
+add_library(tempsense STATIC src/temperature.c src/convert.c src/parse.c src/format.c)
+target_include_directories(tempsense PUBLIC include)
+
+enable_testing()
+add_executable(test_tempsense tests/test_temperature.c)
+target_link_libraries(test_tempsense PRIVATE tempsense)
+add_test(NAME tempsense COMMAND test_tempsense)