Ensure captors only fire when invocation satisfies when/verify

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@jamestalmage made a good catch in #308 that captors could be used with td.when but it was undocumented and it would also capture values when the rest of the rehearsal did not match the actual args. This was effectively a requirements miss, but because our goal is to have td.when and td.verify to behave as symmetrically as possible, it's something we needed to fix.

James implemented a fix in #310, but I had three quibbles with it: (a) it broadened awareness of "capturing" to matchers themselves, even though captors are a one-off subset, (b) it expanded the private namespace claimed by matchers with __capture, and (c) it didn't verify that an argument was a matcher before invoking __capture.

• Commit James' failing tests
• implement an afterSatisfaction hook to the matcher creation, which only fires after all args match on an invocation or verification
• document the new hook
• make the new behavior work for the in-place rewrite that's still (slowly) underway; right now that means https://github.com/testdouble/testdouble.js/blob/master/src/when/index.js needs to be analyzed and updated with this responsibility

Fixes #310
Fixes #308

[searls]

By the way, I've intentionally chosen not to document this td.when support for argument captors right now. If you're simply capturing a value (as opposed to a function), I think argThat is usually more succinct & local. If you're capturing a function, then td.callback is often more appropriate. I can't think of a place where I'd explicitly recommend it over other constructs provided by the lib

[searls]

Also dependency CI appears to be broken. Disabling

[searls]

Landed in 3.2.7