add: *SelectSQL.IterContext is returns iter.Seq2[*, error].

[mackee]

Description

This PR adds a new IterContext method to the generated code.

Key Features:

• IterContext returns iter.Seq2[{{ row struct }}, error] and a closer.
• Allows processing rows one by one using the syntax: for row, err := range rows.
• When combined with github.com/BooleanCat/go-functional/v2/it's TryCollect, it can retrieve results similar to AllContext.
• Enables the use of for range in scenarios where you want to filter query results or transform them into another type.