Upgrade to xxhash 0.8.2 as a Conan requirement, enable SIMD hashing (#4893)

We are currently using old version 0.6.2 of `xxhash`, as a verbatim copy and paste of its header file `xxhash.h`. Switch to the more recent version 0.8.2. Since this version is in Conan Center (and properly protects its ABI by keeping the state object incomplete), add it as a Conan requirement. Switch to the SIMD instructions (in the new `XXH3` family) supported by the new version.

conanfile.py

@@ -36,6 +36,7 @@ class Xrpl(ConanFile):
         'soci/4.0.3',
         'sqlite3/3.42.0',
         'zlib/1.2.13',
+        'xxhash/0.8.2',
         'wasmedge/0.11.2',
     ]
 
@@ -86,6 +87,7 @@ class Xrpl(ConanFile):
         'soci:shared': False,
         'soci:with_sqlite3': True,
         'soci:with_boost': True,
+        'xxhash:shared': False,
     }
 
     def set_version(self):
@@ -159,4 +161,5 @@ class Xrpl(ConanFile):
             'openssl::crypto',
             'date::date',
             'grpc::grpc++',
+            'xxHash::xxhash',
         ]