Add TXG timestamp database

This feature enables tracking of when TXGs are committed to disk,
providing an estimated timestamp for each TXG.

With this information, it becomes possible to perform scrubs based
on specific date ranges, improving the granularity of data
management and recovery operations.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Reviewed-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Signed-off-by: Mariusz Zaborski <mariusz.zaborski@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Closes #16853

include/sys/spa_impl.h

@@ -55,6 +55,8 @@
 #include <sys/dsl_deadlist.h>
 #include <zfeature_common.h>
 
+#include "zfs_crrd.h"
+
 #ifdef	__cplusplus
 extern "C" {
 #endif
@@ -344,6 +346,12 @@ struct spa {
 	spa_checkpoint_info_t spa_checkpoint_info; /* checkpoint accounting */
 	zthr_t		*spa_checkpoint_discard_zthr;
 
+	kmutex_t	spa_txg_log_time_lock;	/* for spa_txg_log_time */
+	dbrrd_t		spa_txg_log_time;
+	uint64_t	spa_last_noted_txg;
+	uint64_t	spa_last_noted_txg_time;
+	uint64_t	spa_last_flush_txg_time;
+
 	space_map_t	*spa_syncing_log_sm;	/* current log space map */
 	avl_tree_t	spa_sm_logs_by_txg;
 	kmutex_t	spa_flushed_ms_lock;	/* for metaslabs_by_flushed */