Refine structured error handler typing

[abdulselamadillmohammed]

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1. What GitHub issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes SNOW-3246741: Align structured error-handler typing and ready-exception handling #2790

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am modifying authorization mechanisms
   • I am adding new credentials
   • I am modifying OCSP code
   • I am adding a new dependency

3. Please describe how your code solves the related issue.

   This change aligns the connector’s structured error-handling API with the contract already used in errors.py.

   It introduces a shared structured payload type for error details and a shared protocol for error handlers, then applies that contract to the sync connection and cursor errorhandler attributes. It also narrows the structured error-handler flow to Snowflake Error subclasses only.

   In addition, it updates errorhandler_wrapper_from_ready_exception() so generic Python exceptions are re-raised directly instead of being routed into the dict-based structured handler path. This avoids the inconsistent case described in SNOW-3246741: Align structured error-handler typing and ready-exception handling #2790, where non-Snowflake exceptions could enter a handler flow that expects structured error details.

   The PR also adds unit tests covering:
   - default structured error handling
   - forwarding structured payloads to custom handlers
   - normalization of ready Error instances
   - direct re-raise behavior for generic exceptions

4. (Optional) PR for stored-proc connector:

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Please add changelog entry in DESCRIPTION.md

[abdulselamadillmohammed]

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[abdulselamadillmohammed]

I’ve added a changelog entry in DESCRIPTION.md. Please let me know if anything else is needed or if you have any feedback.