add automatic json conversion for attributes #543

Job	Run time
build	2m 57s
Julia 1.6 - ubuntu-latest - x64	3m 30s
Julia 1.6 - macOS-latest - x64	5m 24s
Julia 1.6 - windows-latest - x64	12m 37s
Julia 1.7 - ubuntu-latest - x64	4m 18s
Julia 1.7 - macOS-latest - x64	6m 51s
Julia 1.7 - windows-latest - x64	4m 32s
Julia nightly - ubuntu-latest - x64	4m 12s
Julia nightly - macOS-latest - x64	5m 46s
Julia nightly - windows-latest - x64	6m 39s
	56m 46s

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