Use JSON as the wire format in Gearman jobs #1606

Job	Run time
Lint	1m 45s
Test frontend	24s
Test mcp-server on 3.8	6m 9s
Test mcp-server on 3.9	5m 25s
Test mcp-server on 3.10	9m 3s
Test mcp-server on 3.11	7m 28s
Test mcp-server on 3.12	9m 2s
Test mcp-client on 3.8	9m 36s
Test mcp-client on 3.9	9m 26s
Test mcp-client on 3.10	8m 44s
Test mcp-client on 3.11	8m 52s
Test mcp-client on 3.12	9m 27s
Test dashboard on 3.8	9m 3s
Test dashboard on 3.9	9m 35s
Test dashboard on 3.10	9m 5s
Test dashboard on 3.11	6m 24s
Test dashboard on 3.12	10m 47s
Test archivematica-common on 3.8	8m 9s
Test archivematica-common on 3.9	8m 15s
Test archivematica-common on 3.10	9m 9s
Test archivematica-common on 3.11	8m 17s
Test archivematica-common on 3.12	9m 27s
Test storage-service on 3.9	5m 24s
Test migrations on 3.9	5m 17s
	3h 4m 13s

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