chore: Improve error

[luoyuxia]

Purpose

Linked issue: close #63

Brief change log

Tests

API and Format

Documentation

[Copilot]

Pull request overview

This PR improves error handling in the Fluss Rust client by migrating from thiserror to snafu for error definitions and introducing structured API error responses from the Fluss server. The changes enable more detailed error context and better integration with the server's error reporting protocol.

Key Changes:

• Migrated error definitions from thiserror to snafu with structured error variants containing message and source fields
• Implemented Fluss API error protocol by adding FlussError enum, ApiError struct, and error response parsing in RPC headers
• Updated all error instantiation sites across the codebase to use the new structured error format

Reviewed changes

Copilot reviewed 38 out of 38 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
crates/fluss/Cargo.toml	Added snafu dependency for structured error handling
crates/fluss/src/error.rs	Migrated from thiserror to snafu; restructured error variants with message/source fields; added From trait implementations
crates/fluss/src/rpc/fluss_api_error.rs	New file implementing FlussError enum with 57 error codes and ApiError struct for server API errors
crates/fluss/src/rpc/mod.rs	Exposed error module and FlussError/ApiError types publicly
crates/fluss/src/rpc/error.rs	Added RpcDecodeError variant for protobuf decode errors
crates/fluss/src/rpc/frame.rs	Added ProtoErrorResponseDecodeError variant for error response decoding
crates/fluss/src/rpc/message/header.rs	Implemented error response parsing in ResponseHeader; added error_response field
crates/fluss/src/rpc/server_connection.rs	Updated request method to check for API errors in response headers and convert to FlussAPIError
crates/fluss/src/proto/fluss_api.proto	Added ErrorResponse protobuf message definition
crates/fluss/src/rpc/message/*.rs	Split ReadError/WriteError imports and added explicit error mapping with map_err
crates/fluss/src/metadata/*.rs	Updated error instantiations from tuple variants to struct variants with message field
crates/fluss/src/row/datum.rs	Updated RowConvertError instantiations to use struct variant
crates/fluss/src/io/*.rs	Updated error instantiations to structured format with descriptive messages
crates/fluss/src/client/**/*.rs	Updated all error handling to use new structured error variants
crates/fluss/tests/integration/admin.rs	Added test_fluss_error_response test to verify API error handling

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