Support Avro writes, defaults, and custom partition locations for native Format Tables

[JingsongLi]

Summary

Extend native Format Table read and write behavior to match the Java implementation:

• Read catalog-managed partitions at their registered custom locations. Canonicalize filesystem identities and reject traversal, table-directory overlap, and overlapping partition ownership before listing files.
• Write Avro object container files with Java-compatible nullable, logical, and nested schemas. Stream completed Avro blocks to storage, honor avro.codec and file.block-size, and expose Avro through the existing format writer factory.
• Apply schema column defaults after input nullability validation and before partition routing or file projection, matching Java's DefaultValueRow order.
• Treat a resolved catalog partition root as a complete partition regardless of its filesystem path depth, so hidden staging directories are excluded.

Verification

• cargo test -p paimon --lib format_ --quiet (94 passed)
• cargo test -p paimon-datafusion --test rest_format_table_scan --quiet (12 passed)
• cargo test -p paimon-datafusion --test rest_format_table_dml --quiet (9 passed)
• cargo test -p paimon --lib file_block_size --quiet (1 passed)
• cargo clippy -p paimon --lib -- -D warnings
• cargo fmt --all -- --check
• git diff --check

The commit adds 2,054 lines, including behavioral tests for Avro round trips, default values, and catalog location failure paths.

[leaves12138]

LGTM. Re-reviewed with a focus on Java parity. Verified integer default truncation and overflow handling against 1,356 executed Java cases, rechecked ARRAY and TIMESTAMP defaults through Java Avro readback, and ran the Rust unit suite plus 35 focused DataFusion regression tests. The previous findings are addressed; no blocking issues found. The CI check is green; the remaining CI jobs should complete before merging.