Extract all statistics logging-related fields from __wt_connection_impl (lines 874-886) into a new WT_CONN_STAT_LOG structure. This includes stat_session, stat_tid, stat_tid_set, stat_cond, stat_format, stat_fs, stat_json_tables, stat_path, stat_sources, stat_stamp, and stat_usecs. Access will be via conn->stat_log.<field>.

Files affected

• src/include/connection.h — Define WT_CONN_STAT_LOG structure and replace individual stat fields
• src/conn/conn_stat.c — Update all statistics logging code
• src/support/stat.c — Update any statistics access patterns
• Any files that reference statistics logging infrastructure

Definition of Done

• New WT_CONN_STAT_LOG structure defined in connection.h containing all statistics logging fields
• All stat logging fields removed from __wt_connection_impl and replaced with single stat_log member
• All references updated from conn->stat_session to conn->stat_log.session, etc.
• Code compiles cleanly with no warnings
• All existing tests pass
• Grep confirms no stale references to old stat logging field paths