Try lifting Session<Action = _> bounds into impl for better errors

[plaidfinch]

Currently, the Action for methods on Chans is restricted in the where-clause of the methods themselves. This means that errors involving session type mismatches restate the full session type of the expected session in a way that can be hard to parse. It's possible that moving this bound upward to the enclosing impl block for each method would cause these errors to be easier to read. This change will require each method to be enclosed in its own impl block.

Upsides:

• better error messages?

Downsides:

• documentation will become more verbose, because there will be more separate impl blocks
• potentially it won't actually improve error messages?

[yaymukund]

I do not think this is better 🥲

Before	After

I've pushed my work to https://github.com/boltlabs-inc/dialectic/compare/better-error-experiment in case you wanna doublecheck.

[plaidfinch]

Following up on this since we talked about it verbally: I agree with you, sadly. Thanks for trying it out!