Add ReadAsBytes to IScenarioResult

[kgkoutis]

Closes #248

IScenarioResult has no binary accessor. Every reader on it decodes the body as text, so an endpoint returning a file, image or PDF cannot be asserted on. ScenarioResult.Read<T>(Func<Stream, T>) does the right thing and is public, but it lives on the concrete class rather than the interface Scenario(...) returns, so callers have to downcast to reach it.

Change

byte[] ReadAsBytes();
Task<byte[]> ReadAsBytesAsync();

on IScenarioResult, implemented on ScenarioResult through the existing Read/ReadAsync helpers. That means they inherit the same behaviour as the other readers: the body is rewound before and after, so a scenario can assert on the bytes and still call ReadAsJson<T>() afterwards — covered by one of the tests.

This adds members to a public interface and so breaks external implementors. It follows the ReadAsServerSentEvents precedent from the v9 beta (#239) of adding readers straight to the interface rather than via a default implementation. Happy to switch to a default implementation instead if you would rather not spend the break — say the word.

Tests

Three acceptance tests in specs_against_aspnet_core_app, alongside the existing Bug_92_repeated_reads_of_the_response cases:

• read_the_response_as_bytes
• read_the_response_as_bytes_async
• reading_as_bytes_does_not_consume_the_response

Full Alba.Testing suite passes locally on net10.0: 666 tests, 0 failures.

Docs

IScenarioResult is inside the sample_IScenarioResult region, so the interface listing on the docs site picks the new members up when the snippets tool runs. A v9_CHANGELOG.md entry is included under New features.

Motivation

Found while adding integration tests for two endpoints that stream an .xlsx. The test now parses the response with ClosedXML and asserts a sheet name, so a truncated or corrupt stream fails rather than passing on the content type alone — that needed the bytes.