Add opt-in connect timeout support to SDK HTTP client (#56)

[chrismshea]

Summary

Adds opt-in support for a Guzzle connect timeout to the SDK's HTTP client, and documents the timeout exception surface. Backward-compatible: the default request timeout (30s) is unchanged, and no connect timeout is applied unless one is configured.

Motivation: the SDK is called synchronously in user-facing contexts (e.g. the Magento extension's add-to-cart path). With only a total request timeout and no connect timeout, a slow or unreachable API can block a request and tie up web/PHP workers. This adds the fast-fail lever for the unreachable-host case, and clarifies why a timeout is not caught by HttpException.

Changes

• Http.php — new $connectTimeout constructor argument (default 0). When > 0, it is applied as Guzzle RequestOptions::CONNECT_TIMEOUT; when 0, no connect timeout is set, preserving prior behavior for existing consumers.
• Sdk.php — new connect_timeout config key (default 0), plumbed to Http. Config docblock now documents api_request_timeout, connect_timeout, and the timeout exception surface.
• HttpTest.php — 2 new tests asserting the client receives CONNECT_TIMEOUT only when configured.

Exception surface (documented in Sdk.php)

A Guzzle request/connect timeout raises GuzzleHttp\Exception\ConnectException / RequestException, which is not response-based and is therefore not represented by SubscribePro\Exception\HttpException (which requires a ResponseInterface). Consumers that must handle timeouts should catch the Guzzle transfer exceptions (or \RuntimeException) in addition to HttpException.

Backward compatibility

• Default api_request_timeout remains 30.
• connect_timeout defaults to 0 (disabled) — existing consumers see no behavior change.
• The new Http constructor arg is optional and last-positional.

Testing

• vendor/bin/phpunit tests/HttpTest.php → 20/20 pass (18 existing + 2 new).
• Verified end-to-end in a Magento 2.4.8 environment: an unreachable API with connect_timeout=1 fails at ~1.0s with a ConnectException (confirming the connect timeout is applied).

Related

• Consumer-side counterpart (config override + frontend impact): Lower default SP API timeout for frontend calls; support connect timeout subscribepro-magento2-ext#306
• A follow-up here could add opt-in Guzzle retry middleware for transient blips (see Gracefully handle SP API timeouts across remaining synchronous storefront call sites subscribepro-magento2-ext#307).

Closes #56