refactor: split up poll_transmit into per_path and per_space parts

[dignifiedquire]

Starts to split up poll_transmit into per_path and per_space parts.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.44061% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.99%. Comparing base (1240596) to head (7f91667).

Files with missing lines	Patch %	Lines
quinn-proto/src/connection/mod.rs	85.21%	38 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #255      +/-   ##
==========================================
- Coverage   76.01%   75.99%   -0.03%     
==========================================
  Files          81       81              
  Lines       22569    22626      +57     
==========================================
+ Hits        17156    17194      +38     
- Misses       5413     5432      +19     

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[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/quinn/pr/255/docs/iroh_quinn/

Last updated: 2026-01-07T11:18:32Z

[divagant-martian]

We do need this is some form, this is a good option. At some point I thought whether we should to per path, per space, or per space and per path (nesting ordering) and ofc with the current code the correct answer is path and then space. The thing is that this is consequence of a "bad" code design (the best we could come up with at the beginning) because paths are spaces.

So I'm wondering if we should instead take the route of modeling spaces correctly as:
Initial, Handshake, Path(PathId)
which to my initial questioning, is a single loop.

I'm worried taking this route would make it harder to move in that direction. I also don't want to stop this in favor a non existent better way we don't really (yet) know how hard it is to achieve.

Or perhaps this is actually a good intermediate step to get there?

Keen to hear y'alls thoughts

[dignifiedquire]

Or perhaps this is actually a good intermediate step to get there?

I would argue, even if we want to move to making paths, spaces, this approach already helps and will make life easier for everyone in the meantime