Default value for CLEAR_EXPIRED_TOKENS_BATCH_INTERVAL

[n2ygk]

@merito Sorry this is after the fact but wouldn't a default value of 0 be best, especially since the sleep is always executed even if the batch is tiny.
https://github.com/merito/django-oauth-toolkit/blob/725c3c9d8927379c9808abd1badb4fcd9ff1cbaa/oauth2_provider/models.py#L636

Originally posted by @n2ygk in #969 (comment)

[n2ygk]

I was enhancing and running the clear_expired tests and noticed that the test was taking .4 sec longer than it should have;-)

[folt]

Can you describe what problem you are trying to solve with this PR?

[n2ygk]

@folt The recently-added default value is to add a sleep of 0.2 seconds, causing all users who haven't explicitly overridden the default to incur a .2 second sleep -- even if only clearing a single expired token. The sleep is always called after the batch of tokens is cleared.

Setting the default to 0 makes the default behavior match prior behavior before batching was added.

Does this explain the reason sufficiently?

[n2ygk]

@folt to further clarify, here's the code snippet:
https://github.com/jazzband/django-oauth-toolkit/blob/ac201526843ff63ad3861bb37e4099521cff091a/oauth2_provider/models.py#L630-L637