feat: add support for guzzlehttp/psr7 3.x and Guzzle 8

[HecFranco]

Summary

• Widen guzzlehttp/psr7 to allow ^3.0 and guzzlehttp/promises to allow ^3.0, enabling installs alongside Guzzle 8.
• Update GuzzleTracingMiddleware to resolve HTTP responses via method_exists(..., 'getResponse') instead of a hard dependency on Guzzle 7's RequestException, so tracing works with both Guzzle 7 and Guzzle 8 exception types.
• Keep existing Guzzle 7 behavior intact while remaining compatible with Guzzle 8's exception hierarchy.

Test plan

• Install the SDK with Guzzle 7 and confirm tracing middleware still attaches status codes from RequestException responses
• Install with Guzzle 8 / guzzlehttp/psr7 3.x and confirm Composer resolves successfully
• Exercise failed Guzzle 8 requests through GuzzleTracingMiddleware and verify response status is captured when getResponse() is available
• Run the existing PHPUnit suite for tracing / Guzzle-related coverage

Made with Cursor

[HecFranco]

Thank you for taking the time to review this contribution.

This PR adds compatibility with guzzlehttp/psr7 3.x and Guzzle 8 while preserving existing Guzzle 7 behavior. I would greatly appreciate your review and approval when you have a moment.

Please let me know if any changes or additional coverage would be helpful. Happy to iterate based on your feedback.