fix(http-client): expose types to allow naming HttpClient with middleware

[soul022]

Summary

This PR addresses #1590 by re-exporting the internal types that compose the HttpClient generic stack.

Currently, when a user applies middleware using HttpClientBuilder, the resulting type becomes a complex chain, such as HttpClient<MyMiddleware<RpcService<HttpBackend>>>. While some of these structs were marked pub, they were located in private modules, making it impossible for users to explicitly name the type in function signatures or struct definitions.

Example Usage

Before this change, the following code would fail to compile because RpcLogger, RpcService, and HttpBackend were not reachable:

use jsonrpsee::http_client::{HttpClient, RpcService, HttpBackend, RpcLogger, RpcServiceBuilder};

// Explicitly naming the default client type
fn get_client() -> HttpClient<RpcLogger<RpcService<HttpBackend>>> {
    HttpClient::builder()
        .build("http://localhost:9933")
        .unwrap()
}

// Naming a client with stripped/custom middleware
fn get_custom_client() -> HttpClient<RpcService<HttpBackend>> {
    HttpClient::builder()
        .set_rpc_middleware(RpcServiceBuilder::new())
        .build("http://localhost:9933")
        .unwrap()
}

Fixes

Closes #1590

[jsdw]

Do you remember why you added this feature everywhere?

[soul022]

Here I added serde/alloc because cargo hack CI runs with --no-default-features, and without it jsonrpsee-types fails to compile - serde's Cow and Box impls require the alloc feature when std isn't enabled. this was a latent issue that this PR's CI exposed.

[jsdw]

Ok sounds fair to me; I wonder why it came up now and not before hand.

[soul022]

this is probably because cargo hack is exercising --no-default-features + async-client (and other combos) that don’t get hit in the usual workspace test run. Also, CI is on rustc 1.92.0 now, which changes diagnostics formatting, so a few try build fixtures needed refresh