Implement basic calloc and add unit test for it (#26)

## Description

Implement basic calloc and add unit test for it

## Issues

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Closes #22 

<!-- use if this PR is linked but should not close the issue -->

Related: #<issue-number>

## Testing

Calloc unit test

Author: felixnagele

src/calloc.cpp

@@ -6,9 +6,22 @@ namespace mem
 
 void* calloc(size_t num, size_t size)
 {
-    (void)num;
-    (void)size;
-    return nullptr;
+    size_t total_size = num * size;
+    size_t overflow_check = total_size / num;
+    if (overflow_check != size && num > 0 && size > 0)
+    {
+        return nullptr;
+    }
+
+    void* memory_allocation = malloc(total_size);
+    if (!memory_allocation)
+    {
+        return nullptr;
+    }
+
+    memset(memory_allocation, 0, total_size);
+
+    return memory_allocation;
 }
 
 } // namespace mem

tests/unit/test_calloc.cpp

@@ -0,0 +1,17 @@
+#include "malloc_from_scratch/memory_allocator.h"
+#include "test_utils.h"
+
+int main()
+{
+    size_t amount = 10;
+    void* ptr = mem::calloc(amount, sizeof(int));
+    ASSERT_NOT_NULL(ptr);
+
+    int* arr = static_cast<int*>(ptr);
+    for (int i = 0; i < amount; i++)
+    {
+        ASSERT_TRUE(arr[i] == 0);
+    }
+
+    TEST_PASS();
+}