Add handling for long-running Senzing calls

[spompea-cfa]

Add an environment variable SZ_CALL_TIMEOUT_SECONDS and supporting timeout logic so
that Senzing calls that continue past the timeout are abandoned (and logged as errors).
(Note that a Senzing call cannot ever actually be cancelled.) In the future we may want to
revisit / reevaluate this approach.

Also add logic to restore visibility (in SQS) to the currently-in-light message if/when the Consumer
receives a SIGINT / SIGTERM signal.

[Copilot]

Pull Request Overview

Adds timeout handling for long-running Senzing calls to prevent indefinite blocking and implements graceful cleanup logic for process termination signals.

• Introduces configurable timeout mechanism using SIGALRM to abandon Senzing calls that exceed the specified timeout
• Updates SQS message visibility timeout to match the Senzing call timeout for better queue management
• Adds signal handlers for SIGINT/SIGTERM to restore message visibility before process termination

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

File	Description
middleware/timeout_handling.py	New module implementing alarm-based timeout mechanism with custom exception
middleware/redoer.py	Adds timeout wrapper around process_redo_record calls with error handling
middleware/consumer.py	Adds timeout wrapper around add_record calls and signal handlers for graceful shutdown
README.md	Documents the new SZ_CALL_TIMEOUT_SECONDS environment variable

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[jamesiarmes]

Looks good overall. I like seeing the SIGINT/SIGTERM handling.