Added xxHash, a very fast non-cryptographic hash algorithm, to the crypto extension.

Changed the SHA2 implementation.

All extensions are now built with the -O3 optimization level.

⚠️ Renamed build artifacts:

• sqlean-linux-x86.zip → sqlean-linux-x64.zip
• sqlean-macos-x86.zip → sqlean-macos-x64.zip

⚠️ Dropped support for 32-bit Windows.