feat: mark partially-covered lines in yellow

So far lines that are covered but have missing function calls
(instantiations) were marked with red. To better indicate that they're
basically called but have a few missing instantiations a new yellow
color is introduced for those.

assets/index.css

@@ -130,6 +130,10 @@
     @apply bg-red-400 hover:bg-red-500 dark:bg-red-800 dark:hover:bg-red-700;
   }
 
+  .partially-covered {
+    @apply bg-yellow-400 hover:bg-yellow-500 dark:bg-yellow-800 dark:hover:bg-yellow-700;
+  }
+
   .gutter.covered {
     @apply bg-green-400 dark:bg-green-800 !important;
   }
@@ -138,6 +142,10 @@
     @apply bg-red-400 dark:bg-red-800 !important;
   }
 
+  .gutter.partially-covered {
+    @apply bg-yellow-400 dark:bg-yellow-800 !important;
+  }
+
   .page-footer {
     @apply text-sm font-bold pl-4 pt-4;
   }

templates/source.html

@@ -50,8 +50,10 @@
         {% match coverage %}
           {% when Coverage::Covered(_) %}
             {% let class = "covered" %}
-          {% when Coverage::Uncovered(_) %}
+          {% when Coverage::Uncovered(0) %}
             {% let class = "uncovered" %}
+          {% when Coverage::Uncovered(_) %}
+            {% let class = "partially-covered" %}
           {% when Coverage::Unknown %}
             {% let class = "" %}
         {% endmatch %}