fix(mocknet): make stream deadline methods noop instead of returning error

[walldiss]

Summary

• Make SetDeadline, SetReadDeadline, and SetWriteDeadline on mocknet streams return nil instead of an error
• Mocknet uses io.Pipe which doesn't support deadlines, but returning an error breaks callers that treat SetWriteDeadline failure as fatal
• Since writes on in-memory pipes complete immediately, deadline enforcement is unnecessary and the noop is safe

Context

go-libp2p-pubsub added SetWriteDeadline calls in handleSendingMessages (part of libp2p/go-libp2p-pubsub#631). The deadline error is treated as fatal. The stream is reset and the hello packet is never sent. This prevents gossipsub peers from discovering each other's subscriptions in any mocknet-based test.

[MarcoPolo]

We recently released the simlibp2p package under x/simlibp2p. That's the preferred way to simulate networks in tests as it supports everything a real QUIC transport supports and properly models congestion.

I think we should deprecate our mocknet package. We aren't using it anywhere within go-libp2p, and I don't want to spend time maintaining it when we have a better alternative.

That said, I don't strongly oppose the general idea here, and I'm a bit surprised it's taken this long to find this issue.

Since writes on in-memory pipes complete immediately, deadline enforcement is unnecessary and the noop is safe

Deadlines aren't only about how fast writes happen. They protect a node from peers that are (possibly maliciously) stalling a stream.

These changes wouldn't work for testing those cases. But maybe that's fine

[Wondertan]

This is a quick way to solve the issue that doesn't require major testing refactoring. We are aware of simnet and that mocknet looms with deprecation.

[MarcoPolo]

Please gofmt the file @walldiss, and we can merge this.

[walldiss]

There seems to be some CI issue related to testing setup: go: go.mod requires go >= 1.25.7 (running go 1.24.13;. @MarcoPolo anything needed from my end?

[MarcoPolo]

nope, that's a known issue that I haven't had a chance to fix it.

[MarcoPolo]

thanks for the PR