rpc: add request and response interceptors for middleware support

[samuelarogbonlo]

Summary

Implements request and response interceptor pattern for RPC clients, enabling rate limiting, logging, and other middleware functionality for WebSocket/IPC connections.

Motivation

Fixes #33221

Users need a way to implement rate limiting and other cross-cutting concerns for RPC clients, particularly for WebSocket/WSS connections. This was requested in [issue link].

Changes

• Added RequestInterceptor and ResponseInterceptor types
• Implemented WithRequestInterceptor() and WithResponseInterceptor() client options
• Hooked interceptors into all RPC methods: CallContext, BatchCallContext, Notify, Subscribe
• Request interceptors run before sending (ideal for rate limiting, validation)
• Response interceptors run after receiving (ideal for logging, metrics, error wrapping)
• Supports chaining multiple interceptors

Design decisions:

• Batch calls: interceptors run once per batch (transport-level), per-item errors in BatchElem.Error
• Follows gRPC/Connect RPC interceptor patterns
• Zero performance impact when not configured

Testing

• Added 11 comprehensive tests covering all RPC methods
• Tests verify interceptor chaining, error handling, and batch behavior
• All tests passing

Breaking Changes

None - purely additive API

[samuelarogbonlo]

@fjl Please kindly comment as to why this was closed