clean up implementation of `Node`

[ralexstokes]

simplify trait impls to expose a "bytes-like" thing normalize fmt impls for hex-printing

[codecov[bot]]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (20829ed) 75.73% compared to head (b5b13cc) 75.71%.

:exclamation: Current head b5b13cc differs from pull request most recent head c026da1. Consider uploading reports for the commit c026da1 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #112 +/- ## ========================================== - Coverage 75.73% 75.71% -0.02% ========================================== Files 17 17 Lines 849 869 +20 ========================================== + Hits 643 658 +15 - Misses 206 211 +5 ``` | [Files](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes) | Coverage Δ | | |---|---|---| | [ssz-rs/src/merkleization/mod.rs](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes#diff-c3N6LXJzL3NyYy9tZXJrbGVpemF0aW9uL21vZC5ycw==) | `89.77% <ø> (ø)` | | | [ssz-rs/src/merkleization/node.rs](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes#diff-c3N6LXJzL3NyYy9tZXJrbGVpemF0aW9uL25vZGUucnM=) | `100.00% <100.00%> (+42.85%)` | :arrow_up: | | [ssz-rs/src/serde.rs](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes#diff-c3N6LXJzL3NyYy9zZXJkZS5ycw==) | `69.56% <100.00%> (ø)` | | | [ssz-rs/src/utils.rs](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes#diff-c3N6LXJzL3NyYy91dGlscy5ycw==) | `86.36% <80.00%> (+36.36%)` | :arrow_up: | | [ssz-rs/src/list.rs](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes#diff-c3N6LXJzL3NyYy9saXN0LnJz) | `70.23% <0.00%> (-5.41%)` | :arrow_down: | | [ssz-rs/src/vector.rs](https://app.codecov.io/gh/ralexstokes/ssz-rs/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Stokes#diff-c3N6LXJzL3NyYy92ZWN0b3IucnM=) | `72.09% <0.00%> (-7.40%)` | :arrow_down: |

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