Update to stream responses without dependency on react/promise-stream

[clue]

This changeset updates the client to stream responses without the dependency on react/promise-stream. It now uses a small internal ReadableUnwrapStream in place of unwrapReadable() and buffers streams with a few lines of its own, so consumers of this package no longer install the extra package. The dependency was added with #27 back in 2016, and reactphp/http#482 removed it from the HTTP layer the same way.

All APIs and streaming behavior stay the same, so this should be safe to apply. Stream events now only pass the arguments documented for ReadableStreamInterface, without the extra stream argument the old package appended. The tests are ported from react/promise-stream v1.7.0 and the test suite confirms this keeps 100% code coverage. This should also make it easier to fix #96 in a follow-up PR.

Builds on top of #27 and reactphp/http#482
Refs #106 and #96

[Copilot]

🟡 Changes recommended

Pending resume requests can leave inputs stalled, and buffering cancellation retains accumulated output.

2 open issues

• Pending resume is lost for initially paused streams · New
• Cancelled buffering retains accumulated stream output · New

What changed in this PR

Replaces react/promise-stream with internal helpers for Docker response streaming and buffering.

Changes:

• Adds an internal promise-backed readable stream.
• Implements buffering and cancellation without the removed dependency.
• Ports stream tests and updates functional tests.

File	Description
tests/​Io/​StreamingParserTest.php	Tests buffering, errors, and cancellation.
tests/​Io/​ReadableUnwrapStreamTest.php	Tests the new stream wrapper.
tests/​FunctionalClientTest.php	Uses internal buffering in integration tests.
src/​Io/​StreamingParser.php	Replaces external streaming helpers.
src/​Io/​ReadableUnwrapStream.php	Adds the internal readable-stream wrapper.
src/​Client.php	Uses the wrapper for logs and attachment.
composer.json	Removes react/promise-stream.

_{Review effort: Balanced}