zinject: count matches and injections for each handler

When building tests with zinject, it can be quite difficult to work out
if you're producing the right kind of IO to match the rules you've set
up.

So, here we extend injection records to count the number of times a
handler matched the operation, and how often an error was actually
injected (ie after frequency and other exclusions are applied).

Then, display those counts in the `zinject` output.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Closes #16938

include/sys/zfs_ioctl.h

@@ -23,7 +23,7 @@
  * Copyright (c) 2012, 2024 by Delphix. All rights reserved.
  * Copyright 2016 RackTop Systems.
  * Copyright (c) 2017, Intel Corporation.
- * Copyright (c) 2024, Klara, Inc.
+ * Copyright (c) 2024-2025, Klara, Inc.
  */
 
 #ifndef	_SYS_ZFS_IOCTL_H
@@ -421,6 +421,8 @@ typedef struct zinject_record {
 	uint64_t	zi_nlanes;
 	uint32_t	zi_cmd;
 	uint32_t	zi_dvas;
+	uint64_t	zi_match_count;		/* count of times matched */
+	uint64_t	zi_inject_count;	/* count of times injected */
 } zinject_record_t;
 
 #define	ZINJECT_NULL		0x1