More efficient utils.chunk

[Abdeldjalil-H]

The utils.chunk function from tortoise.utils is converting instances into list. I think it is better to not load all the list at one time but rather in chunks as the name suggested. This is useful in cases when the user passes a generator instead of list especially for large datasets.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 9058250244

Details

• 10 of 10 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 87.943%

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Totals
Change from base Build 9028420328:	0.01%
Covered Lines:	5776
Relevant Lines:	6472

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💛 - Coveralls

[Abdeldjalil-H]

It seems that the failing tests have nothing to do with the changes made, because the changed part is not being called at all for the failed test case. Moreover, it passes the first time, then when I changed contrubitors file it fails!