Switch internal byte to internal u64 abstraction #1740

Job	Run time
docs	3m 7s
nightly	3m 2s
msrv	1m 33s
clippy	1m 47s
rustfmt	16s
basics	1s
test_lib	3m 35s
test_doc	6m 7s
build_feature (alloc)	3m 27s
no_std (ubuntu-latest, minimal)	1m 9s
build_feature (cli)	4m 3s
no_std (macos-latest, minimal)	1m 42s
test_miri (rune, runtime:: hir::arena:: --skip runtime::vm:: --skip runtime::vm_execution:: )	3m 3s
build_feature (cli,doc)	3m 58s
test_rune	2m 20s
test_miri (rune-alloc)	6m 8s
build_feature (cli,fmt)	3m 51s
build_feature (doc)	3m 53s
wasm	1m 5s
build_feature (workspace)	3m 30s
build_feature (languageserver)	4m 7s
build_feature (byte-code)	3m 28s
build_feature (capture-io)	3m 26s
build_feature (emit)	3m 24s
	1h 12m 2s

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