TRCLI-266: Attachments not 'attached' to the test in the test run, for AutomationID (code first) tests

[acuanico-tr-galt]

Issue being resolved: #421

Solution description

The as_completed() function returns futures in the order they complete, not in submission order, to resolve this we
store responses by request ID and reconstruct in original order.

Changes

Modified handle_futures() in api_request_handler.py to:

• Store responses in a dictionary keyed by request body id()
• Reconstruct responses in original request order before returning
• This ensures zip() in result_handler.py pairs requests with their correct responses

We also optimized attachments uploading to use Threadpool executor, also updated progress tracking displayed in the standard output.

Potential impacts

None. Changes introduced are backwards compatible.

Steps to test

1. Upload more than 500 test cases (preferably with attachments)
2. There should be no mapping error once uploaded to TestRail.

PR Tasks

• PR reference added to issue
• README updated
• Unit tests added/updated