Switch internal byte to internal u64 abstraction #1739

Job	Run time
clippy	1m 55s
msrv	1m 42s
nightly	3m 2s
docs	3m 16s
rustfmt	8s
basics	1s
no_std (ubuntu-latest, minimal)	1m 14s
no_std (macos-latest, minimal)	1m 23s
test_lib	2m 30s
test_doc	5m 47s
build_feature (alloc)	3m 18s
test_miri (rune, runtime:: hir::arena:: --skip runtime::vm:: --skip runtime::vm_execution:: )	3m 14s
build_feature (cli)	3m 59s
test_miri (rune-alloc)	5m 59s
test_rune	2m 32s
wasm	1m 4s
build_feature (cli,doc)	4m 1s
build_feature (cli,fmt)	4m 9s
build_feature (doc)	3m 33s
build_feature (workspace)	3m 29s
build_feature (languageserver)	3m 54s
build_feature (byte-code)	3m 24s
build_feature (capture-io)	3m 27s
build_feature (emit)	3m 23s
	1h 10m 24s

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