Added a few changes to query expressions (#51)

- Added the between operator to query expressions.
- Added the using query expression suffix to specify which index to query (or force a scan). This is required if query planning has found multiple indices that can potentially be used.
- Rewrote the types of the query expressions to allow for functions to be defined once, and be useful in queries that result in DynamoDB queries, and evaluation.
- Added some test functions around time and summing numbers.
- Fixed a bug in the del-attr which was not honouring marked rows in a similar way to set-attr: it was only deleting attributes from the first row.
- Added the -to type flag to set-attr which will set the attribute to the value of a query expression.

internal/common/sliceutils/map.go

@@ -39,3 +39,22 @@ func Filter[T any](ts []T, fn func(t T) bool) []T {
 	}
 	return us
 }
+
+func FindFirst[T any](ts []T, fn func(t T) bool) (returnedT T, found bool) {
+	for _, t := range ts {
+		if fn(t) {
+			return t, true
+		}
+	}
+	return returnedT, false
+}
+
+func FindLast[T any](ts []T, fn func(t T) bool) (returnedT T, found bool) {
+	for i := len(ts) - 1; i >= 0; i-- {
+		t := ts[i]
+		if fn(t) {
+			return t, true
+		}
+	}
+	return returnedT, false
+}