Replace `Instance.termination_reason` values with codes #5619

Job	Run time
compute-version	2s
build-docs / build-docs	3m 11s
build-artifacts / frontend-build	8s
build-artifacts / runner-test (ubuntu-latest)	55s
build-artifacts / gateway-build	9s
build-artifacts / runner-test (macos-latest)	1m 37s
build-artifacts / code-lint	48s
build-artifacts / python-build	0s
build-artifacts / python-test	0s
build-artifacts / generate-json-schema	-1s
build-artifacts / runner-compile (ubuntu-24.04-arm, linux, arm64)	36s
build-artifacts / runner-compile (ubuntu-24.04, linux, amd64)	38s
upload-pre-pypi-artifacts	0s
upload-post-pypi-artifacts	-1s
	8m 2s

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