Fix floats on Wasm

On wasm32, terms are aligned by 4 bytes. `memory_heap_allocation` returns a pointer for `n` terms.
We used float_term_t to create an union between a term and float. However, floats are aligned to 8 bytes which made
casting between union and term pointers unsafe.

We replaced union usage to `memcpy` which allows unaligned memory access. The true solution would be to return
correctly aligned memory from memory_heap_alloc but fix for that would need a lot more testing.

Signed-off-by: Jakub Gonet <jakub.gonet@swmansion.com>

Author: jgonet

src/libAtomVM/term.h

@@ -2331,16 +2331,18 @@ static inline term term_from_float(avm_float_t f, Heap *heap)
     term *boxed_value = memory_heap_alloc(heap, FLOAT_SIZE);
     boxed_value[0] = ((FLOAT_SIZE - 1) << 6) | TERM_BOXED_FLOAT;
 
-    float_term_t *boxed_float = (float_term_t *) (boxed_value + 1);
-    boxed_float->f = f;
-
+    // For wasm32, alignof(avm_float_t) = 8 and alignof(term) = 4
+    // `memory_heap_alloc` returns memory aligned to term size.
+    memcpy(boxed_value + 1, &f, sizeof(avm_float_t));
     return ((term) boxed_value) | TERM_PRIMARY_BOXED;
 }
 
 static inline avm_float_t term_to_float(term t)
 {
-    const float_term_t *boxed_float = (float_term_t *) (term_to_const_term_ptr(t) + 1);
-    return boxed_float->f;
+    avm_float_t result;
+    // see `term_from_float`
+    memcpy(&result, term_to_const_term_ptr(t) + 1, sizeof(avm_float_t));
+    return result;
 }
 
 static inline bool term_is_number(term t)