Refactor libdovi structs

[quietvoid]

Benchmark results, after refactor and switching to bitstream-io:

parse_single_unspec62_nalu/profile5.bin
                        time:   [1.5488 µs 1.5499 µs 1.5514 µs]
                        change: [-38.907% -38.381% -37.947%] (p = 0.00 < 0.05)
                        Performance has improved.

parse_single_unspec62_nalu/profile8.bin
                        time:   [1.5595 µs 1.5601 µs 1.5606 µs]
                        change: [-40.566% -40.390% -40.248%] (p = 0.00 < 0.05)
                        Performance has improved.

parse_single_unspec62_nalu/fel_orig.bin
                        time:   [3.5473 µs 3.5685 µs 3.5966 µs]
                        change: [-35.236% -34.024% -33.139%] (p = 0.00 < 0.05)
                        Performance has improved.

parse_single_unspec62_nalu/mel_variable_l8_length13.bin
                        time:   [2.3935 µs 2.3954 µs 2.3980 µs]
                        change: [-37.822% -37.750% -37.680%] (p = 0.00 < 0.05)
                        Performance has improved.

parse_single_unspec62_nalu/cmv40_full_rpu.bin
                        time:   [1.9724 µs 1.9729 µs 1.9736 µs]
                        change: [-39.689% -39.079% -38.656%] (p = 0.00 < 0.05)
                        Performance has improved.

parse_single_unspec62_nalu/unordered_l8_blocks.bin
                        time:   [3.9151 µs 3.9409 µs 3.9679 µs]
                        change: [-34.045% -33.831% -33.629%] (p = 0.00 < 0.05)
                        Performance has improved.

rewrite_single_unspec62_nalu/fel_orig.bin
                        time:   [6.6318 µs 6.6365 µs 6.6423 µs]
                        change: [-50.041% -49.998% -49.960%] (p = 0.00 < 0.05)
                        Performance has improved.

rewrite_single_unspec62_nalu/mel_variable_l8_length13.bin
                        time:   [4.6305 µs 4.6349 µs 4.6420 µs]
                        change: [-52.047% -51.964% -51.892%] (p = 0.00 < 0.05)
                        Performance has improved.