feat(cli-tools): Binary publish

[teogeb]

Added a --binary flag to the stream subscribe and stream publish commands. When this flag is enabled, the commands read and write binary bytes instead of normal JSON or hex strings. If the --with-metadata flag is also used, the bytes represent the protobuf-encoded StreamMessage objects.

All messages use a length-prefixed frame format: each item is prefixed with a 4-byte header indicating the frame length.

A new --raw flag was added to stream publish, allowing protobuf binary messages to be sent exactly as provided. Currently this flag is supported only when both --binary and --with-metadata are used, since raw publishing requires StreamMessage objects as input.

Helpers

These existing helpers may be useful when working with the new features introduced in this PR:

• convertStreamMessageToBytes() and convertBytesToStreamMessage() from @streamr/sdk can be used to convert between StreamMessage objects and their protobuf byte form
• toLengthPrefixedFrame() and LengthPrefixedFrameDecoder from @streamr/utils can be used to create and parse length-prefixed frames

Related changes

Added MessageSigner export to the SDK. This class is required in stream-publish.test.ts.

Refactored the CLI tool’s startCommand test utilities so that they can capture either text or binary output.

Future improvements

We could support --raw publishing without the --binary flag by constructing StreamMessage instances directly in the CLI tool. See stream-publish.test.ts for an example of how to create messages.