refactor(iroh): remove flume from iroh-cli and iroh (#2543)

## Description

refactor(iroh): remove flume from iroh-cli and iroh

Removes most usages of flume from iroh and all usages of flume from
iroh-cli.

## Breaking Changes

None

## Notes & open questions

Note: this does not remove all usages because we need the iroh docs
purge PR to be merged before that.

## Change checklist

- [ ] Self-review.
- [ ] ~~Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.~~
- [ ] ~~Tests if relevant.~~
- [ ] ~~All breaking changes documented.~~

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Co-authored-by: Philipp Krüger <[email protected]>
Co-authored-by: Kasey <[email protected]>
Co-authored-by: Kasey Huizinga <[email protected]>