fix(proto): Use path PTOs for PATH_ABANDON calculations

[matheus23]

Description

This changes the PTO calculations for the deadline by which we expect PATH_ABANDONs to arrive as well as when we can discard a path.

Concretely:

• We expect the PATH_ABANDON to be reciprocated by 3 * PTO of the path that we send the PATH_ABANDON on
• After the above timeout happens, or after receiving a PATH_ABANDON, we wait for another 3 * PTO of the path that's abandoned to discard the path state.

Waiting 3 * PTO for a response on a particular path is pretty standard procedure, so this makes sense for PATH_ABANDON as well. By moving the code to where the PATH_ABANDON is actually sent we make sure that we know which path the PATH_ABANDON is sent on.

Waiting 3 * PTO to discard the path state is similar to the time that's used for draining connections: This is the best effort at making sure there's no more stray datagrams flying around.

We still avoid setting a time for an expected PATH_ABANDON receive, because that timer might fire incorrectly when the path was abandoned just before the connection severs. We don't know if the peer actually ignored it, or if it's due to packet loss.

[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/quinn/pr/291/docs/iroh_quinn/

Last updated: 2025-12-19T16:16:43Z

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.29412% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.53%. Comparing base (200a68a) to head (8702e44).

Files with missing lines	Patch %	Lines
quinn-proto/src/connection/mod.rs	95.18%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
+ Coverage   76.33%   76.53%   +0.20%     
==========================================
  Files          81       83       +2     
  Lines       22962    23363     +401     
==========================================
+ Hits        17528    17881     +353     
- Misses       5434     5482      +48     

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