test(p2p): cover the timer branch of waitForDialTime

[tbruyelle]

Description

Follow-up to #6054, from AviaOne's review. The test is theirs; I folded it in as a subtest and verified it.

runDialLoop parks on waitForDialTime, which wakes on three things:

select {
case <-ctx.Done():      // covered: "the wait ends on context cancellation"
case <-timer.C:         // not covered
case <-sw.dialNotify:   // covered: "a due item is dialed while an earlier one backs off"
}

The timer branch had no coverage, and the gap was invisible — removing case <-timer.C: left the entire package green:

$ # with `case <-timer.C:` deleted from waitForDialTime
$ go test ./tm2/pkg/p2p/
ok      github.com/gnolang/gno/tm2/pkg/p2p    0.238s

That branch is not cosmetic. Without it, a backed off item is never dialed once it becomes due: the loop parks until something else is queued or the node shuts down, so persistent peer backoff silently stops retrying. It is the behaviour #6054 exists to provide.

The test

Added as a third subtest of TestMultiplexSwitch_DialLoop_BackedOff, so the three subtests now map one to one onto the three select branches.

A single item is queued, due shortly, with nothing else in the queue and a live context — so the timer is the only thing that can bring the loop back.

Verification

Mutation checked in both directions:

	new subtest	other two subtests	DoesNotSpin	package
case <-timer.C: removed	FAIL	pass	pass	FAIL
unmodified master	pass	pass	pass	pass

So the subtest is the one carrying the guarantee, and nothing else in the suite notices that branch going missing. Passing run repeated with -count=3; gofmt, go vet and ./tm2/pkg/p2p/... all clean.

Test-only, so no ADR per AGENTS.md.

---

Drafted with AI assistance (Claude Code). I have reviewed the change and the verification and stand behind them.

[Gno2D2]

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