Support reading skims from Parquet files, in addition to OMX #299

Job	Run time
linux-64-py	6m 3s
Estimation Notebooks Test	54m 57s
Standard 1-Zone Example (MTC)	1h 7m 15s
macOS	12m 42s
Estimation Mode Unit Tests	24m 29s
Expression Profiling Tests	6m 38s
estimation_edb_creation_test	6m 43s
Standard 2-Zone Example (SANDAG)	1h 21m 13s
random_seed_generation_test	3m 8s
placeholder_psrc	46m 45s
prototype_mtc	1h 2m 15s
placeholder_multiple_zone	5m 34s
prototype_mtc_extended	1h 44m 20s
win-64	16m 40s
production_semcog	5m 7s
prototype_mwcog	56m 34s
develop-docbuild	0s
	9h 20m 23s

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