Do not use wildcard pub re-export

[haerdib]

This can easily lead to exports of the same named struct, such as Error and co (see #424 (comment)).

A cleaner way would be to re-export everything that should be public specifically.

[clangenb]

When I tried to integrate the refactored api-client into the worker, I thought that the exports are in general kind of a chaos.

[echevrier]

Check wildcard re-export and re-export only "important" items (for example used in the examples) to make them easily searchable/accessible in the public API

• check that the new path is unique, at every export level (no conflict with another item from other modules)
• check if the "privacy chain" is short-circuited by re-exproting them
• check the exported public API

[echevrier]

Note:
JsonrpseeClient API:

• substrate_api_client::rpc::JsonrpseeClient
• substrate_api_client::rpc::SubscriptionWrapper

WsRpcClient API:

• substrate_api_client::rpc::WsRpcClient
• substrate_api_client::rpc::subscription::WsSubscriptionWrapper

TungsteniteRpcClient API:

• substrate_api_client::rpc::TungsteniteRpcClient`
• substrate_api_client::rpc::TungsteniteSubscriptionWrapper`