benchmark: provide a handwritten N=1 implementation for InsertAndDelete

As I had expected, this removes an unfair disadvantage for Oblast, which
had to maintain two differently-typed slices for Insert() and Delete().
This is not really a fair comparison since usually you would not be
doing both operations in one go.

For Gorp, this rewrite is neutral. But in a shocking twist, Gorm somehow
does _significantly_ worse with a specialized N=1 implementation:

```
BenchmarkInsertAndDelete/N=1/via_Gorm-24
before: 11508 B/op    157 allocs/op
after:  12840 B/op    172 allocs/op
```

1 files changed, 29 insertions, 0 deletions

diff --git a/benchmark/benchmark_test.go b/benchmark/benchmark_test.go
index 439ecaf..12f739c 100644
--- a/benchmark/benchmark_test.go
+++ b/benchmark/benchmark_test.go
@@ -285,6 +285,16 @@ func BenchmarkInsertAndDelete(b *testing.B) {
 				}
 				must.Succeed(b, store.Delete(noctx, db, records...))
 			}
+			if batchSize == 1 {
+				insertAndDeleteWithOblast = func(b *testing.B) {
+					record := OblastEntry{Message: "hello"}
+					must.Succeed(b, store.Insert(noctx, db, &record))
+					if record.ID == 0 {
+						b.Errorf("ID was not filled!")
+					}
+					must.Succeed(b, store.Delete(noctx, db, record))
+				}
+			}
 
 			insertAndDeleteWithGorp := func(b *testing.B) {
 				records := make([]any, batchSize)
@@ -299,6 +309,16 @@ func BenchmarkInsertAndDelete(b *testing.B) {
 				}
 				_ = must.Return(gorpDB.Delete(records...))(b)
 			}
+			if batchSize == 1 {
+				insertAndDeleteWithGorp = func(b *testing.B) {
+					record := GorpEntry{Message: "hello"}
+					must.Succeed(b, gorpDB.Insert(&record))
+					if record.ID == 0 {
+						b.Errorf("ID was not filled!")
+					}
+					_ = must.Return(gorpDB.Delete(&record))(b)
+				}
+			}
 
 			insertAndDeleteWithGorm := func(b *testing.B) {
 				records := make([]GormEntry, batchSize)
@@ -315,6 +335,15 @@ func BenchmarkInsertAndDelete(b *testing.B) {
 				assert.ErrEqual(b, result.Error, "<success>")
 				assert.Equal(b, result.RowsAffected, int64(batchSize))
 			}
+			if batchSize == 1 {
+				insertAndDeleteWithGorm = func(b *testing.B) {
+					record := GormEntry{Message: "hello"}
+					must.Succeed(b, gorm.G[GormEntry](gormDB).Create(b.Context(), &record))
+					result := gormDB.Delete(&record)
+					assert.ErrEqual(b, result.Error, "<success>")
+					assert.Equal(b, result.RowsAffected, 1)
+				}
+			}
 
 			insertAndDeleteWithStraightExec := func(b *testing.B) {
 				ids := make([]int64, batchSize)