'During' means that it didn't last all summer, in contrast to 'for the summer, etc, but 'in' would mean much the same to me. I might try to suggest that 'during' is longer, but I'm not entirely convinced.
I worked there during summer.
-->meaning in summer,I worked there for a period of time, not the whole summer.
If I'd like to put the preposition 'in' in this sentence, I think it should be,
I worked there in the summer time.
-->meaning I worked there for an entire summer time.
Is that right?
I worked there in the summer. [It was summer when I worked there. No duration is discussed].
I worked there during the summer. [It was summer when I worked there. A duration is suggested (activity over time) but the length of time is not specified.]
These two could be exactly the same, but "during" suggests a longer period than "in".
If the speaker worked there all summer, then "for the summer" would be more precise. :wink: