Feat CSV source

[ItzNotABug]

Adds the CSV source handler.

[ItzNotABug]

@abnegate here's a quick benchmark -

1. 3 documents in 0.0039 sec.
2. 1,00,000 documents in 5.9281 sec
3. 10,00,000 documents in 65.5917 sec
4. 50,00,000 documents in 318.6609 sec


The controller froze on a CSV with 1,00,00,000 documents but I'll assume its way more than the last set.

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@abnegate
If the insertion order doesn't matter, can we not use coroutines here so its not really sequential?

[abnegate]

Let's add some tests as well

Stale