feat(sf_core): expose structured error diagnostics

[zeroshade]

Summary

• expose wrapper-neutral structured diagnostics through ApiError::diagnostics()
• add a public ErrorDiagnostics object containing vendor code, SQLSTATE, query ID, and request ID
• preserve server-first SQLSTATE behavior plus sf_core's existing vendor-code and login fallbacks
• replace the protobuf converter's three private extraction helpers with the public API
• migrate the existing diagnostic tests to exercise the reusable object

This lets in-process wrappers such as the Rust ADBC driver consume the same normalized diagnostics without matching sf_core's internal RestError variants or duplicating vendor-code/SQLSTATE tests.

Testing

• cargo test -p sf_core --lib — 1698 passed, 1 ignored
• cargo check -p sf_core --all-targets
• cargo check -p sf_core --no-default-features
• cargo clippy -p sf_core --lib — no findings in changed code
• cargo doc -p sf_core --no-deps
• cargo fmt --all -- --check
• git diff --check

[Copilot]

Pull request overview

This PR adds a wrapper-neutral structured diagnostics API to sf_core by introducing ApiError::diagnostics() and a public ErrorDiagnostics type, then refactors the protobuf driver converter to consume that shared API so wrapper implementations can read normalized Snowflake diagnostics without matching internal RestError variants.

Changes:

• Introduces ErrorDiagnostics and ApiError::diagnostics() to surface vendor code, SQLSTATE, query ID, and request ID in a stable, wrapper-friendly shape.
• Updates the protobuf DriverException conversion path to use ApiError::diagnostics() instead of local private extraction helpers.
• Migrates existing diagnostics-focused tests to exercise the new reusable diagnostics object.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
sf_core/src/protobuf/apis/database_driver_v1/converter.rs	Replaces private vendor/query/request ID extraction helpers with ApiError::diagnostics() and updates tests accordingly.
sf_core/src/apis/database_driver_v1/mod.rs	Re-exports ErrorDiagnostics alongside ApiError for wrapper consumption.
sf_core/src/apis/database_driver_v1/error.rs	Adds the ErrorDiagnostics public struct and implements ApiError::diagnostics() with the existing SQLSTATE/vendor-code/login fallback behavior.

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