test/crimson/omap: enlarge values under ASan to shrink depth-driven tests

innernode_split_merge_balancing, omap_iterate, list and monotonic_inc grow
the tree to a fixed depth, so under ASan a larger value reaches the same
depth (same split/merge paths) with far fewer keys. It stays below the
per-kv limit so inserts keep the normal path.

Scale the extent-count bound in innernode_split_merge_balancing with the
value size accordingly.

Signed-off-by: Sun Yuechi <sunyuechi@iscas.ac.cn>