Client reorg follow-up

[CriesofCarrots]

Problem

#27246 splits solana-client so that its constituent clients can be more-easily imported downstream. But some follow-up work would make the arrangement even better.

Proposed Solution

• Replace all monorepo imports of solana-client with specific client crate
• Rework ClientErrorKind so that the common rpc-client-api crate doesn't depend on reqwest
• Rework modules in solana-tpu-client so that quic- and udp-clients can be split to their own modules - started here Add TpuConnectionCache and begin disentangling quic and udp #28080
• Move rpc_client with_spinner methods behind a feature, making indicatif dependency optional
• Consider moving mock_sender to its own crate
• Ask @brson to correct any documentation snafus I made 🙏

[brson]

I'll take another pass at the various client crate docs once #27188 lands.