outworkers / phantom / 1644

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travis-ci

Buffer up fetched rows in the spool (#704)

Rather than wrap each row in a future, carefully trying to prefetch to
avoid blocking, we simply drain the entire fetched page into a seq and
async fetch the next page. This fetch is a prefetch in the sense that it
happens whether the tail of the spool is materialized or not. This
eliminates a lot of branches, simplifies the code and seems to yield a
nice speed up.

Locally on my machine (in ms)

Before:
```
Parameters(size -> 10000): 124.270108
Parameters(size -> 20000): 286.841965
Parameters(size -> 30000): 392.405244
```

After:
```
Parameters(size -> 10000): 61.316181
Parameters(size -> 20000): 153.689973
Parameters(size -> 30000): 250.284154
```

16 of 16 new or added lines in 2 files covered. (100.0%)

2987 of 3547 relevant lines covered (84.21%)

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