Move Byron code to `Ouroboros.Consensus.Byron.ByronHFC` #5255

Job	Run time
Build and test (8.10.7, default, all)	8m 14s
Build and test (9.6.6, default, all)	8m 17s
Build and test (9.10.1, default, all)	8m 14s
Run benchmarks	1s
Deploy documentation to GitHub Pages	1s
	24m 47s

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