Add support for partially decoding arrays

[brendanlensink]

For #106, #104

This PR adds a new convenience container called LossyArray that's meant to help with partially decoding arrays of objects, where you don't want to fail the whole request if one of the objects fails to decode.

I'm still working on getting some convenience finalizes together, but generics are hard 😵 In the meantime, I thought it would be good to get your feedback on how this seems.

Also fixes RetryConfiguration not being marked as Sendable and reformats the README to be a little more accessible

[nbrooke]

This looks reasonable as a starting point, three comments:

• Definitely need to figure out the auto-finalization. As things stand right now, this isn't really an improvement over just using something like BetterCodable at the app layer, where it'll be a win to have it in Netable is if you can get away with NOT having to manually create that result struct or implement finalize.
• I wonder if it's possible to have the API be even more stripped down, like that you don't need to change the types at all, you just have like a "lossyTopLevelArrayDecode" property that defaults to false on requests, and if you override it and set it to true it automatically decodes it as a LossyArray completely internally.
• Worth thinking a little about error reporting for this, it would be ideal if failures of this kind were logged to the log destination in some way.even though the request succeeds.

[brendanlensink]

@nbrooke reworked this to use a new Request param: arrayDecodeStrategy.

This feels a little janky, especially in the SmartUnwrap case... but it's hard for me to tell if that might just be the cost of doing business with all the generics, etc or if there's a way to simplify things a little.