Build a byte buffer over paginated pieces when assembling blobs

[adzialocha]

This removes the maximum limit of allowed blob pieces (for now, we might want to have it back with some sort of configuration interface). This touched upon the pagination logic used to iterate over all pieces, so I decided to just paginate through it in a classic manner, page by page.

On top this uses now the BytesMut struct to efficiently assemble the blob pieces. For the future we might want to do this instead https://github.com/p2panda/aquadoggo/issues/548 to avoid keeping very large blobs in memory.

Closes: #546

📋 Checklist

• [x] Add tests that cover your changes
• [x] Add this PR to the Unreleased section in CHANGELOG.md
• [x] Link this PR to any issues it closes
• [x] New files contain a SPDX license header

[codecov[bot]]

Codecov Report

Patch coverage: 90.62% and no project coverage change.

Comparison is base (edc0b30) 92.50% compared to head (bbec0eb) 92.50%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## http-blob-router #547 +/- ## ================================================= Coverage 92.50% 92.50% ================================================= Files 105 105 Lines 17932 17939 +7 ================================================= + Hits 16588 16595 +7 Misses 1344 1344 ``` | [Files Changed](https://app.codecov.io/gh/p2panda/aquadoggo/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda) | Coverage Δ | | |---|---|---| | [aquadoggo/src/db/stores/blob.rs](https://app.codecov.io/gh/p2panda/aquadoggo/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda#diff-YXF1YWRvZ2dvL3NyYy9kYi9zdG9yZXMvYmxvYi5ycw==) | `97.42% <90.62%> (+0.04%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/p2panda/aquadoggo/pull/547/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda)

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