Fix #1264

[davwil]

What changes are proposed in this pull request?

• WHAT: Fixes TypeError crash in RoundTrip.generate() when handling unparseable API error responses
  and corrects the SDK issue tracker URL in error messages from databricks-sdk-go to databricks-sdk-py

• WHY: When _BaseClient.do() receives string/bytes data, it wraps it in BytesIO for retry/seek support (line 167-169 in _base_client.py). If the API returns an unparseable error response, _unknown_error() creates a RoundTrip object to generate debug information. However, it doesn't pass raw=True, causing _redacted_dump() to be called with the BytesIO object instead of a string. This results in len(body) failing with TypeError: object of type '_io.BytesIO' has no len().

  The fix checks if request.body is a string before calling _redacted_dump(). Non-string bodies (like BytesIO) are now logged as [raw stream], consistent with how raw streams are handled elsewhere in the codebase.

  Fixes #1264

How is this tested?

• Added test_unknown_error_with_bytesio_request_body() in tests/test_errors.py that reproduces the exact scenario from the issue
• Updated 3 existing test cases to use the corrected SDK URL

[github-actions]

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Trigger:
go/deco-tests-run/sdk-py

Inputs:

• PR number: 1265
• Commit SHA: 5cf23e67906efb5c0e5807643da8c3ff4f01c63a

Checks will be approved automatically on success.