perf(index): remove Idx bounds-checks from first + last methods
#17114
| Job | Run time |
|---|---|
| 1m 49s | |
| 3m 1s | |
| 1m 37s | |
| 2m 9s | |
| 2m 2s | |
| 1m 48s | |
| 2m 17s | |
| 1m 41s | |
| 1m 55s | |
| 3m 5s | |
| 2m 7s | |
| 17s | |
| 23m 48s |