Subkernel: pass exceptions to kernel

[Spaqin]

ARTIQ Pull Request

Description of Changes

As discussed in another PR about documentation, it's not the best situation if the subkernel await/message pass throws an exception if it cannot be caught. So the exception is extracted from the message (in a way that's still compatible with ARTIQ-8) and sent to the kernel CPU, taking inspiration from RPC.

One caveat is that at the moment exception raised by subkernel called by another subkernel (k->sk1->sk2*) will still not be handled within the first subkernel. Only the main kernel can handle it at the moment, as subkernels only pass the exception source when one arises, rather than the whole exception data.

Tested with a Kasli 2.0 + 1.1 sat with following code:

from artiq.experiment import *


class ExceptionTest(EnvExperiment):
    def build(self):
        self.setattr_device("core")

    @subkernel(destination=1)
    def simple_return(self):
        raise IndexError("err")
    
    @kernel
    def run(self):
        self.core.reset()
        self.simple_return()
        try:
            subkernel_await(self.simple_return, 1)
        except:
            print("caught")

Type of Changes

	Type
✓	:bug: Bug fix

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