[Feature] Add JsonRpcErrorClassifier for standardized error code interpretation

[limehee]

Problem statement

Applications consuming JSON-RPC responses repeatedly implement ad-hoc logic to interpret error.code values (standard vs server-range vs custom). This creates inconsistency and weakens interoperability.

Proposed solution

Add JsonRpcErrorClassifier utility in jsonrpc-core with:

• deterministic classification for integer error codes:
  • standard (-32700, -32600, -32601, -32602, -32603)
  • server reserved range (-32099..-32000)
  • custom
• helper APIs for common checks (isStandard, isServerRange, isCustom)

Alternatives considered

• Keep this as documentation-only guidance
• Let each integration own its own classifier logic

These alternatives do not provide a reusable canonical implementation.

JSON-RPC behavior impact

No protocol behavior change. This introduces a utility for response handling and diagnostics.

Additional context

• Ensure compatibility with existing JsonRpcResponseErrorCodePolicy concepts.
• Add unit tests for boundaries and all standard code values.