feat: Utilities for doing framed-streaming of car files

[matheus23]

Previously, the only way we supported streaming car files was by passing something that implements AsyncWrite to car-mirror.

This works well, with e.g. iroh-net and quinn, or tokio's TcpSocket, but it doesn't work well with HTTP libraries like reqwest, because they essentially require either something that implements AsyncRead or streams of bytes.

We already support streaming blocks, but only in raw format, in a way that isn't framed and not in the car file format.

This PR adds a public utility stream_car_frames that transforms such a stream of blocks into a stream of bytes, framed in the car file format.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (122f369) 50.00% compared to head (35766d5) 48.21%.

❗ Current head 35766d5 differs from pull request most recent head 251bbc4. Consider uploading reports for the commit 251bbc4 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
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- Coverage   50.00%   48.21%   -1.79%     
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  Files          13       12       -1     
  Lines         560      560              
  Branches      267      268       +1     
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- Hits          280      270      -10     
- Misses         62       69       +7     
- Partials      218      221       +3     

Files	Coverage Δ
car-mirror/src/common.rs	54.26% <0.00%> (-2.76%)	⬇️

... and 2 files with indirect coverage changes