Refactor/foreign assets as thin proxy #2224

Job	Run time
forkless-update-data	0s
collator-selection	0s
forkless-update-no-data	0s
canary	0s
governance	0s
node-only-update	0s
try-runtime	0s
polkadot-types	0s
codestyle / yarn_eslint	1m 5s
codestyle / clippy	2m 43s
codestyle / rustfmt	15s
unit-test / develop	7m 34s
xcm / Prepare execution matrix	24s
yarn-dev / opal	25m 6s
yarn-dev / sapphire	41m 48s
yarn-dev / quartz	41m 29s
yarn-dev / unique	27m 46s
xcm / opal	1h 20m 41s
xcm / quartz	2h 51m 52s
xcm / unique	3h 0m 12s
	9h 40m 55s

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