Add plant listener instruction about ceptr

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We should probably rename the current "listeners" code to "expectations" or something like that to not confuse the two different ways we have pending semtrex matching, one on the flux placed there by receptor designers, vs, listeners that are planted on scapes by other receptors via protocols.
Actually we need a word for the combination of an expectation/action pair. Plan?

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230b23d adds LISTEN instruction, which currently adds a listener to the flux. This should be expanded to have listening source for Event log or Scape too.

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closed and split up un-done stuff into separate tickets.

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btw as of 632fce5 we did the renaming of listener -> expectation