Split loader file into multiple different files

[dpeng817]

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[dpeng817]

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• Definitions from module loader #26546
• Genericize object list functionality to take in all sensors, jobs, schedules #26545
• Genericize object list utils #26535
• Make key iterator property on all asset objects #26534
• Split loader file into multiple different files #26533 👈 (View in Graphite)
• File and test refactor #26532
• Consolidate cacheable methods #26531
• Make asset check coercion explicit in with_attributes #26529
• Further simplify asset checks path #26527
• [rfc] Include specs in asset module loaders #26524
• Use new loader code in checks loaders #26514
• Handle attribute mapping properly #26498
• Simplify module asset loader code path #26484
• Delete extra_source_assets param from assets_from_modules #26494
• master

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