[ refactor ] Improve error handling in `Core` #1104

Job	Run time
initialise	3s
quick-check	5m 33s
macos-bootstrap-chez	1m 41s
nix-bootstrap-chez	2m 22s
ubuntu-bootstrap-chez	1m 20s
ubuntu-bootstrap-racket	2m 4s
ubuntu-self-host-previous-version	10m 14s
windows-bootstrap-chez	4m 4s
ubuntu-self-host-chez	0s
ubuntu-build-api	0s
macos-self-host-chez	0s
ubuntu-self-host-racket	0s
windows-self-host-racket	0s
ub-pack-test-pack	2m 2s
ub-pack-test-lsp	1m 48s
ub-test-elab-util	41s
ub-test-collie	22s
ub-test-frex	3m 47s
ub-test-katla-and-html	3m 46s
	39m 47s

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