fix(stdlib): Ensure consistent marshal representation (#2045)

Co-authored-by: Blaine Bublitz <blaine.bublitz@gmail.com>

Author: ospencer

compiler/test/stdlib/marshal.test.gr

@@ -91,3 +91,5 @@ let truncatedRecord = Bytes.slice(
   )
 )
 assert Result.isErr(unmarshal(truncatedRecord))
+
+assert Marshal.marshal("🌾") == Marshal.marshal("🌾")

stdlib/marshal.gr

@@ -423,8 +423,11 @@ let marshal = (value, buf) => {
 @unsafe
 provide let marshal = value => {
   let valuePtr = fromGrain(value)
-  let buf = allocateBytes(size(valuePtr))
+  let size = size(valuePtr)
+  let buf = allocateBytes(size)
+  Memory.fill(buf + 8n, 0n, size)
   marshal(valuePtr, buf + 8n)
+  ignore(value)
   toGrain(buf): Bytes
 }