Added EcoBytes struct

[imbrem]

Add EcoBytes, which is the same as EcoString but holds a raw byte vector rather than a UTF-8 string; this is implemented by making DynamicVec public.

[codecov-commenter]

Codecov Report

Patch coverage: 71.94% and project coverage change: -6.91 :warning:

Comparison is base (c3fd036) 92.21% compared to head (296c6e7) 85.31%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #23 +/- ## ========================================== - Coverage 92.21% 85.31% -6.91% ========================================== Files 4 4 Lines 1041 1212 +171 ========================================== + Hits 960 1034 +74 - Misses 81 178 +97 ``` | [Impacted Files](https://codecov.io/gh/typst/ecow/pull/23?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst) | Coverage Δ | | |---|---|---| | [src/lib.rs](https://codecov.io/gh/typst/ecow/pull/23?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst#diff-c3JjL2xpYi5ycw==) | `100.00% <ø> (ø)` | | | [src/string.rs](https://codecov.io/gh/typst/ecow/pull/23?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst#diff-c3JjL3N0cmluZy5ycw==) | `78.74% <24.00%> (-8.43%)` | :arrow_down: | | [src/bytes.rs](https://codecov.io/gh/typst/ecow/pull/23?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst#diff-c3JjL2J5dGVzLnJz) | `75.52% <75.52%> (ø)` | | ... and [1 file with indirect coverage changes](https://codecov.io/gh/typst/ecow/pull/23/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst)

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[imbrem]

@reknih any updates on whether I can expect this to be merged? Thanks!

[laurmaedje]

Could you also adjust the README and crate-level docs and briefly show EcoBytes?

[laurmaedje]

Closing this due to inactivity. Feel free to reopen it if you want to continue working on this.