feat: paid retrieval optional + bug fixes

[rvagg]

"paid-retrievals" config option, defaulting to "false" will turn on attempting to retrieve from deals that are non-free. Otherwise, retrieval deals that are not free will be filtered. NOTE this changes the default behaviour such that paid retrievals need to be opted into. This should make paych errors go away.

+Other bug fixes because I wrote a test for this and found some other things along the way!

• There's a closure bug for queries where we are skipping querying some candidates! Potentially missing out on a lot of retrievals (tbh I only learned that golang doesn't capture for loop variables within scope last week)
• Per-miner configs are not using defaults in some places because we're looking directly in the MinerConfigs map rather than calling the MinerConfig() method! I renamed it so it's not such a subtle difference now. The two main results of this are:
  1. There's no default max concurrent per SP! This could explain some complaints we've been getting.
  2. No default timeout for queries or retrievals, which may explain some leaky goroutines and weird resource usage stuff we've been seeing.

[codecov-commenter]

Codecov Report

Base: 13.70% // Head: 20.63% // Increases project coverage by +6.93% :tada:

Coverage data is based on head (c9b80fe) compared to base (1d2d50a). Patch coverage: 82.35% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #126 +/- ## ========================================== + Coverage 13.70% 20.63% +6.93% ========================================== Files 16 16 Lines 2226 2234 +8 ========================================== + Hits 305 461 +156 + Misses 1905 1742 -163 - Partials 16 31 +15 ``` | [Impacted Files](https://codecov.io/gh/application-research/autoretrieve/pull/126?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=application-research) | Coverage Δ | | |---|---|---| | [config.go](https://codecov.io/gh/application-research/autoretrieve/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=application-research#diff-Y29uZmlnLmdv) | `0.00% <0.00%> (ø)` | | | [filecoin/retriever.go](https://codecov.io/gh/application-research/autoretrieve/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=application-research#diff-ZmlsZWNvaW4vcmV0cmlldmVyLmdv) | `37.17% <93.33%> (+37.17%)` | :arrow_up: | | [filecoin/retrieverevents.go](https://codecov.io/gh/application-research/autoretrieve/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=application-research#diff-ZmlsZWNvaW4vcmV0cmlldmVyZXZlbnRzLmdv) | `16.41% <0.00%> (+16.41%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=application-research). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=application-research)

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[rvagg]

I realised I forgot to attach my tests to this cause it was a new file .. done now