Move Byron code to `Ouroboros.Consensus.Byron.ByronHFC` #5267

Job	Run time
Build and test (8.10.7, default, all)	10m 46s
Build and test (9.6.6, default, all)	5m 5s
Build and test (9.10.1, default, all)	3m 58s
Deploy documentation to GitHub Pages	0s
Run benchmarks	0s
	19m 49s

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