[rust] Wire batch statistics into the log batch write and read paths

[leekeiabstraction]

Summary

• Wires the V1 batch statistics collection ([rust] Add V1 batch statistics collection #4011) into the write and read paths. Closes [rust] Batch statistics read wiring #4009, closes [rust] Batch statistics write wiring #4010.
• Write: tables with table.statistics.columns set emit V1 batches carrying the serialized statistics between the header and the records data, mirroring Java's MemoryLogRecordsArrowBuilder. A serialization failure degrades to an empty statistics section rather than failing the batch.
• Read: all three magic versions decode — V1 skips the statistics section, V2 additionally reads the leader epoch and shifts the post-CRC header fields, and unknown magics are rejected. This fixes the Rust reader misparsing V1/V2 batches that Java clients and the server already produce; the writer stays on V0/V1 like Java's client-side builder.
• Refactoring: the Fluss batch framing moved out of arrow.rs into a new log_record_batch.rs, separating the Fluss wire format from Arrow IPC concerns. The Arrow builder's long argument lists collapsed into an ArrowBatchConfig struct.

Test Plan

• A cross-language golden fixture (fluss-common/src/test/resources/encoding/statistics_block.hex) pins the statistics block byte-for-byte across all supported types, nulls, both decimal widths, both timestamp precisions, and float NaN/signed-zero ordering (bounds follow Java's Float.compare semantics, not Arrow's IEEE totalOrder). A new Java test generates it, asserts it and parses it back verifying the decoded bounds; the Rust test reads the same file.
• New unit tests cover V1/V2 encode/decode round trips (append-only and changelog), empty, corrupt and truncated batches, leader epoch reads, unsupported magic, per-column degradation for unsupported column types and the size reserve. cargo test -p fluss-rs --lib passes 707 tests; clippy and fmt are clean; the end-to-end integration test is left to [rust] Filter pushdown integration test #3845.

🤖 AI-assisted changes - reviewed by human developer

[leekeiabstraction]

@fresh-borzoni @platinumhamburg @charlesdong1991 Appreciate a review here 🙏