Extract all tiered storage thread-related fields from __wt_connection_impl (lines 888-898) into a new WT_CONN_TIERED structure. This includes tiered_session, tiered_tid, tiered_tid_set, flush_cond, tiered_cond, tiered_interval, tiered_server_running, flush_ckpt_complete, flush_most_recent, flush_state, and flush_ts. Also include the tieredqh queue from line 732. Note: tiered_lock and flush_tier_lock will remain in WT_CONN_LOCKS (from ticket 1.1). Access will be via conn->tiered.<field>.

Files affected

• src/include/connection.h — Define WT_CONN_TIERED structure and replace individual tiered fields
• src/tiered/*.c — Update all tiered storage code
• src/conn/conn_tiered.c — Update tiered thread management
• Any files that reference tiered storage infrastructure

Definition of Done

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