inspect: detect timeouts from inspector context fallback

Some Process.Wait implementations may format ctx.Err() without preserving the context.DeadlineExceeded sentinel. Keep waitErr as the primary classification source, but fall back to the per-inspector context when Wait returned an error and that context's own deadline fired before any parent deadline. Nil Wait still means natural completion, preserving the existing race-safe behavior.

Covers both Run and RunMulti with regressions for string-wrapped context errors.