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

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   • I am adding a new automated test(s) to verify correctness of my new code
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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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[sfc-gh-turbaszek]

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.

[sfc-gh-turbaszek]

Behavioral change in errorhandler_wrapper_from_ready_exception may bypass custom error handlers

The old implementation of errorhandler_wrapper_from_ready_exception routed all exceptions (including non-Error ones) through hand_to_other_handler, which would forward them to any custom errorhandler set on the cursor or connection. The new code immediately re-raises non-Error exceptions, skipping custom handlers entirely:

# New behavior
if not isinstance(error_exc, Error):
    raise error_exc

vs. the old behavior:

# Old behavior
else:
    error_value = error_exc.args

handed_over = Error.hand_to_other_handler(
    connection, cursor, type(error_exc), error_value,
)
if not handed_over:
    raise error_exc

The callers in cursor.py, aio/_cursor.py, and aio/_result_set.py all use isinstance(_next, Exception) as the guard, meaning arbitrary exceptions could flow in. In practice these exceptions come from Error.errorhandler_make_exception(InterfaceError, ...) in result_batch.py, so they should always be Error subclasses. But if any edge case produces a raw Exception, the behavior change would be user-visible:

1. Custom error handlers on cursor/connection would no longer see the exception
2. The messages list on cursor/connection wouldn't be appended to
3. The exception would bubble up raw instead of going through the handler chain

This is probably safe in practice, but it might be worth calling out explicitly as a deliberate behavior change — especially for anyone relying on custom errorhandler callbacks to intercept all exceptions.