feat: add 32-bit architecture supoort

src/md5.h

@@ -4,9 +4,6 @@
 #include <string>
 #include <cstdint>
 
-static_assert(sizeof(uintptr_t) == 8,
-    "Project only works on 64-bits architecture.");
-
 #ifdef _MSC_VER
 static_assert('\x01\x02\x03\x04' == 0x04030201,
 #else

test/stream.cc

@@ -8,7 +8,7 @@ TEST(md5sum, stream) {
     const auto test_data = build_test_data(256 * 256);
 
     MD5 md5;
-    for (uint64_t size = 1; size <= 256; ++size) {
+    for (uint32_t size = 1; size <= 256; ++size) {
         auto expect = MD5::Hash(test_data.data(), size * 256);
 
         for (int times = 0; times < 256; ++times) {