fix: use i64 for index file size

[XiaoHongbo-Hope]

Purpose

Linked issue: close #585

Rust declared IndexFileMeta.file_size as i32 even though the index-manifest Avro schema and Java Paimon both use a 64-bit long. Rust builders therefore rejected individual index files larger than 2 GiB, while the fast decoder silently narrowed Java-written values.

This change preserves the full signed 64-bit file size across Rust read and write paths.

Brief change log

• Widen IndexFileMeta.file_size and all index-file construction paths from i32 to i64.
• Remove the narrowing cast from the fast index-manifest decoder and clean up redundant downstream conversions.
• Add a regression that round-trips i32::MAX + 1 through Avro OCF and the fast decoder.
• Keep checked conversions from u64 and usize so values above i64::MAX still fail explicitly.

Tests

• cargo fmt --all -- --check
• cargo test --locked -p paimon --lib — 1800 passed, 1 ignored
• cargo test --locked -p paimon-datafusion --test system_tables test_table_indexes_system_table -- --exact
• cargo clippy --locked -p paimon -p paimon-c -p paimon-datafusion --all-targets -- -D warnings

API and Format

This changes the public Rust type of IndexFileMeta.file_size from i32 to i64, so downstream source code with explicit i32 construction must be updated.

The storage format does not change: _FILE_SIZE remains an Avro long. Existing manifests remain compatible, and Java can read values written by this change. Older Rust readers still cannot correctly read values above i32::MAX and should be upgraded.

_ROW_COUNT remains unchanged in this focused PR because widening it affects a broader set of row-count and vector-index APIs.

Documentation

No documentation update is required.

[JingsongLi]

+1