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ARROW-12254: [Rust][DataFusion] Stop polling limit input once limit is reached

# Rationale
Once the number of rows needed for a limit query has been produced, any further work done to read values from its input is wasted.

The current implementation of LimitStream will keep polling its input for the next value, and returning `Poll::Ready(None)` , even once the limit has been reached

For queries like `select * from foo limit 10` used for initial data exploration this is very wasteful.

# Changes

This PR changes `LimitStream` so that it drops its input once the limit has been reached -- this both potentially frees resources (memory, file handles, etc) it also avoids unnecessary computation

Closes #9926 from alamb/alamb/limit_less_run

Authored-by: Andrew Lamb <andrew@nerdnetworks.org>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>