Switch internal byte to internal u64 abstraction #1741

Job	Run time
nightly	3m 5s
docs	3m 11s
msrv	1m 39s
clippy	1m 50s
rustfmt	12s
basics	1s
test_lib	3m 30s
test_doc	5m 55s
no_std (ubuntu-latest, minimal)	1m 12s
build_feature (alloc)	3m 20s
test_miri (rune, runtime:: hir::arena:: --skip runtime::vm:: --skip runtime::vm_execution:: )	3m 7s
test_rune	2m 11s
no_std (macos-latest, minimal)	1m 52s
build_feature (cli)	4m 4s
test_miri (rune-alloc)	5m 56s
build_feature (cli,doc)	3m 53s
wasm	1m 0s
build_feature (cli,fmt)	4m 9s
build_feature (doc)	3m 29s
build_feature (workspace)	3m 21s
build_feature (languageserver)	3m 54s
build_feature (byte-code)	3m 15s
build_feature (capture-io)	3m 30s
build_feature (emit)	3m 41s
	1h 11m 17s

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