But if you're expecting another dev to always be available to help you with a review, then they're the ones having to "context-switch", interrupting their own work.
The reality is context-switching is something that comes with the territory if you're working as part of a team developing software. Which isn't to say there aren't opportunities to minimise the disruption it causes, but the idea that you can more or less eliminate it seems like wishful thinking. Perhaps there's a case for minimising it for more junior devs that aren't as capable of dealing with it, though it's equally possible younger brains are better at it!
I think maybe we're using different definitions of the term "context-switch". Certainly it's an interruption, but I don't really think that sitting down with another engineer to do a focused code review where they've already written out a PR description and thought hard about the problem is comparable to starting a brand new branch or picking it up after a while away and trying to juggle 2, 3, or 4 in-progress tickets.
It requires a mental switch in focus. For me anyway, it's not a big difference if it's between working on implementing feature A then switching to working on implementing feature B, and working on feature A then switching to doing a code review for feature B, but I probably take my code reviewing responsibilities more seriously than most (e.g. I always checkout the branch locally, ensure it builds and runs etc.).