BREAKING CHANGE: buffers exposed as binary, as a UTF-8 string

[kafka1991]

Overview

This change introduces a minor breaking API change.

In preparation for follow-up work, the ILP buffer will change from always internally serializing to a UTF-8 string to serializing to binary data.

This PR changes the API to allow this, without changing any of the functionality or wire format.

Detail

The APIs that exposes the buffer in Rust (.as_str()), C (line_sender_buffer_peek) and C++ (buffer::peek()) have been changed to return a binary buffer.

In Rust specifically, the .as_str() method has been renamed to .as_bytes().

This PR closes #89

Internally this change swaps Buffer's backing from a String to a Vec<u8>.

[amunra]

Nearly there!
Some data type inaccuracies to correct and very minor code cleanup required.

[kafka1991]

Nearly there! Some data type inaccuracies to correct and very minor code cleanup required.

Thanks for your review!

[amunra]

A few more changes needed.

Now that the code has specific support for C++20 the CI tests should compile and run with both C++17 and C++20.

[kafka1991]

A few more changes needed.

Now that the code has specific support for C++20 the CI tests should compile and run with both C++17 and C++20.

Already add c++20 CI tests in pipeline

[amunra]

Some more minor changes and one question regading C++14 (which we might have previously supported).

[kafka1991]

Some more minor changes and one question regading C++14 (which we might have previously supported).

We didn't support C++14(or lower) since string_view is introduced in c++17

[amunra]

Looking good!