rust: write attachments in parts (#1285)

### Changelog

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rust: support writing attachments in multiple chunks

### Docs

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### Description

This change supports writing large attachments to MCAP files without the
need to load them into memory.

Currently, in order to write an attachment, you need to load the entire
file into memory, create an `Attachment` record, then use that with the
`attach` method on the writer.
This means that it is not possible to attach files when the file exceeds
the available memory on the computer.

This change adds The methods `start_attachment`, `put_attachment_bytes`
and `finish_attachment` for interactively writing an attachment without
needing to buffer the file in memory. It looks like this:

```rust
let writer = Writer::new(..);
let attachment_length = ..;
let header = AttachmentHeader { .. };

writer.start_attachment(attachment_length, header)?;
writer.put_attachment_bytes(..)?;
writer.put_attachment_bytes(..)?;
writer.put_attachment_bytes(..)?;
writer.finish_attachment()?;
```

I've updated the current `attach` method to use this approach and the
roundtrip tests pass. I've also added some tests for using this API
directly.

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changes. Pretend you are advocating for this change and the reader is
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validate this change. -->

<table><tr><th>Before</th><th>After</th></tr><tr><td>

attachments must be loaded into memory to be written

<!--before content goes here-->

</td><td>

attachments can be written in parts

<!--after content goes here-->

</td></tr></table>

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foxglove/repo#1234` to auto-close the Github issue or Fixes: FG-### for
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---------

Co-authored-by: james-rms <james@foxglove.dev>

rust/Cargo.toml

@@ -7,7 +7,7 @@ categories = [ "science::robotics", "compression" ]
 repository = "https://github.com/foxglove/mcap"
 documentation = "https://docs.rs/mcap"
 readme = "README.md"
-version = "0.12.1"
+version = "0.13.0"
 edition = "2021"
 license = "MIT"
 

rust/src/lib.rs

@@ -89,6 +89,14 @@ use thiserror::Error;
 
 #[derive(Debug, Error)]
 pub enum McapError {
+    #[error("tried to write to output while attachment is in progress")]
+    AttachmentInProgress,
+    #[error("tried to write bytes to an attachment but no attachment was in progress")]
+    AttachmentNotInProgress,
+    #[error("tried to write {excess} more bytes to attachment than the requested attachment length {attachment_length}")]
+    AttachmentTooLarge { excess: u64, attachment_length: u64 },
+    #[error("tried to finish writing attachment but current length {current} was not expected length {expected}")]
+    AttachmentIncomplete { current: u64, expected: u64 },
     #[error("Bad magic number")]
     BadMagic,
     #[error("Footer record couldn't be found at the end of the file, before the magic bytes")]