expose ClickHouse error code and name on raised exceptions

[joe-clickhouse]

Summary

Server errors only carried a formatted message string, so callers had to regex-parse it to branch on the ClickHouse error code. The code was already available in the X-ClickHouse-Exception-Code header and discarded.

• Add code and name attributes to the Error base class, inherited by DatabaseError and OperationalError. Callers can now branch on exc.code == 60 instead of parsing the message.
• Populate code from the exception header in both the sync and async error handlers. It is set even when show_clickhouse_errors is disabled, since the numeric code is not sensitive.
• Populate name with the symbolic error name such as UNKNOWN_TABLE, parsed from the response body and gated behind show_clickhouse_errors. It is read from the full body before truncation so a small max_error_size does not drop it.
• The human readable message string is unchanged. Both fields default to None when unavailable, for example on transport errors.

Closes #786

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG

[Copilot]

Pull request overview

This PR enhances the driver’s exception model so ClickHouse server-side HTTP errors expose structured metadata (code and name) on raised exceptions, avoiding brittle regex parsing of formatted message strings.

Findings (ordered by severity):

• Minor test maintainability nit: one unit test mutates a private settings dict directly instead of using the public common.get_setting/common.set_setting helpers.

Changes:

• Add code (numeric) and name (symbolic) attributes to the Error base exception, inherited by DatabaseError / OperationalError.
• Populate code from X-ClickHouse-Exception-Code in both sync and async HTTP error handlers; populate name from the response body when show_clickhouse_errors is enabled.
• Add unit + integration tests covering code/name extraction and truncation behavior; document the feature in the changelog.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
clickhouse_connect/driver/exceptions.py	Adds code/name fields on the base error type plus helpers to parse code/name from header/body.
clickhouse_connect/driver/httpclient.py	Sync HTTP error handler now parses and attaches structured code/name to raised exceptions.
clickhouse_connect/driver/asyncclient.py	Async HTTP error handler now parses and attaches structured code/name to raised exceptions.
tests/unit_tests/test_driver/test_httpclient.py	Adds sync/async unit tests asserting structured fields (and truncation behavior).
tests/unit_tests/test_driver/test_exceptions.py	Adds focused unit tests for parsing helpers and exception field defaults.
tests/integration_tests/test_client.py	Adds integration coverage verifying structured fields are present on real server errors.
CHANGELOG.md	Documents the new structured error fields and their gating behavior.