Fix common.h Memory Alignment Issue

[JaredTate]

This PR fixes a memory alignment issue detected by compiling with built in address sanitizer. It appears this file was not properly merged during the 8.22 process as BTC core had already fixed this. This is an important file used throughout the entire codebase.

The older file led to undefined behavior when ptr is not guaranteed to be 4-byte-aligned (for a uint32_t), or 8-byte-aligned (for a uint64_t). Many compilers and platforms allow unaligned reads if you compile with certain flags, but the C++ standard does not guarantee it is safe—and AddressSanitizer flags it.

Although on many x86 processors unaligned loads won’t crash at runtime, the C/C++ standard still considers it undefined behavior. UBSan/ASan is telling you that you are violating strict aliasing/alignment guarantees.

The simplest fix is to replace & use memcpy.

To discover this I compiled with this setting for ./configure:

./configure CXXFLAGS="-g -O1 -fno-omit-frame-pointer" --enable-debug --with-sanitizers=address,undefined

Running the c++ tests shows this fail right away:

Applying these fixes, re-running it no longer fails. Wallet compiles, runs and without sanitizer all 470 tests pass. However there are other issues with memory still to fix.

Note: This flow works well for memory debugging:

1. Compile with ./configure + sanitizer checks
2. Run c++ tests with: src/test/test_digibyte
3. Read out put & fix bugs
4. Rerun tests to confirm no issues
5. Recompile with ./configure alone without sanitizer
6. Re run src/test/test_digibyte and make sure all 470 tests pass
7. Compile Qt, open let it run to make sure all wallet behaviour is normal

[gto90]

utACK

[ycagel]

cACK