fix: preserve snapshot ID width in UseRef

[fallintoplace]

Summary

• keep UseRef() snapshot IDs as int64_t while resolving refs
• add a regression test for a ref pointing at INT32_MAX + 42

Root Cause

TableScanBuilder::UseRef() copied SnapshotRef::snapshot_id into an int32_t, even though snapshot IDs are modeled as int64_t in refs, metadata lookup, and scan context.

Testing

• uvx cmake --build build --target scan_test -j 8
• ./build/src/iceberg/test/scan_test --gtest_filter=*UseRefPreservesInt64SnapshotIds*
• ./build/src/iceberg/test/scan_test

Fixes #660

[wgtmac]

Good catch! Thanks for fixing this!