[codex] fix unsupported attachment error mapping

[cotovanu-cristian]

Summary

• Add a typed UiPathUnsupportedAttachmentError with stable UNSUPPORTED_ATTACHMENT_FORMAT error_code.
• Map Bedrock Converse unsupported MIME ValueError chains into that typed UiPath error.
• Preserve MIME type and provider detail for downstream agent-specific mapping.
• Bump uipath-llm-client to 1.15.1 because 1.15.0 already exists without this API.

Root cause

Bedrock Converse request conversion can reject file blocks locally with a bare ValueError containing Unsupported MIME type before an HTTP response exists. The generic provider wrapper previously mapped that to the root UiPathError, losing the user-actionable attachment semantics.

Validation

• uv run pytest tests/langchain/features/test_exception_wrapping.py -q
• uv run ruff check src/uipath/llm_client/init.py src/uipath/llm_client/utils/exceptions.py tests/langchain/features/test_exception_wrapping.py
• uv run ruff format --check src/uipath/llm_client/init.py src/uipath/llm_client/utils/exceptions.py tests/langchain/features/test_exception_wrapping.py
• git diff --check