fix: move int128_t and uint128_t aliases into the iceberg namespace (#972)

The aliases were declared at global scope in the public header iceberg/util/int128.h. Any consumer that includes an iceberg header then gets global int128_t and uint128_t names, which conflict with other libraries or application code that define the same names. All uses in the project are already inside namespace iceberg, so this change is source compatible within the project.

Co-authored-by: Rohan Jain <rohanjain@microsoft.com>

Author: rohanjain101

src/iceberg/util/int128.h

@@ -24,11 +24,18 @@
 
 #if defined(_MSC_VER)
 #  include <__msvc_int128.hpp>
+#elif !defined(__GNUC__) && !defined(__clang__)
+#  error "128-bit integer type is not supported on this platform"
+#endif
+
+namespace iceberg {
+
+#if defined(_MSC_VER)
 using int128_t = std::_Signed128;
 using uint128_t = std::_Unsigned128;
-#elif defined(__GNUC__) || defined(__clang__)
+#else
 using int128_t = __int128;
 using uint128_t = unsigned __int128;
-#else
-#  error "128-bit integer type is not supported on this platform"
 #endif
+
+}  // namespace iceberg