Add sandbox_c cmake project + ccache workflow for pool testing

sandbox_c/tests/test_temperature.c

@@ -0,0 +1,26 @@
+#include "temperature.h"
+#include <assert.h>
+#include <math.h>
+#include <string.h>
+#include <stdio.h>
+
+int main(void) {
+    assert(fabs(to_fahrenheit(0.0) - 32.0) < 1e-9);
+    assert(fabs(to_fahrenheit(100.0) - 212.0) < 1e-9);
+
+    Reading r;
+    assert(parse_reading("{\"sensor\":\"attic\",\"celsius\":21.50}", &r) == 0);
+    assert(strcmp(r.sensor, "attic") == 0);
+    assert(fabs(r.celsius - 21.5) < 1e-9);
+    assert(parse_reading("{\"celsius\":-300.0}", &r) == 0);
+    assert(fabs(clamp_to_absolute_zero(r.celsius) + 273.15) < 1e-9);
+    assert(parse_reading("nonsense", &r) != 0);
+
+    char buf[128];
+    Reading in = { "boiler", 65.25 };
+    assert(format_reading(&in, buf, sizeof buf) == 0);
+    assert(strstr(buf, "\"sensor\":\"boiler\"") != NULL);
+
+    puts("all tempsense assertions passed");
+    return 0;
+}