[core] Support reading sequence_number in AuditLogTable and BinlogTable

[wzhero1]

Purpose

This PR adds support for accessing system fields (specifically sequence_number) in AuditLogTable and BinlogTable.

Currently, downstream consumers often need the sequence_number to ensure strict ordering or to implement exactly-once processing when reading from audit logs or binlogs. However, these system tables previously did not expose this field.

This change implements KeyValueSystemFieldsRecordReader to enable the projection of system fields for KeyValue records, allowing users to query sequence_number directly from audit log and binlog tables.

Tests

• Added IncrementalReadSystemFieldsTest to verify functionality.
• Updated AuditLogTableTest and BinlogTableTest to cover sequence_number read cases.

API and Format

• No change to storage format.
• No public API change.

Documentation

• No documentation change required.