Feat/jrpc engine v2

[lwin-kyaw]

Motivation and Context

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Description

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project. (run lint)
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My code requires a db migration.

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Note

Medium Risk
Adds a new JSON-RPC processing path and changes shared error serialization logic, which could affect middleware behavior and error shapes if adopted by consumers.

Overview
Introduces a new src/jrpc/v2 JSON-RPC engine and server API, including JsonRpcEngineV2, JsonRpcServer, and a frozen MiddlewareContext, with stricter semantics around request vs. notification handling, immutability, and middleware composition/destroy lifecycle.

Adds a V1↔V2 bridge via asLegacyMiddleware plus cloning/context propagation helpers, and updates error handling to better preserve/serialize cause data for JSON-RPC errors (with deterministic toString). Extensive new vitest coverage is added for the v2 engine/server, compatibility layer, and error serialization behavior.

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