Add native Solana program feature

[Rhovian]

Summary

Adds a native feature for non-Anchor, non-Pinocchio Solana programs:

• keeps solana-v3 as the existing Solana version selector
• adds native = ["solana-v3"] as a first-class account/runtime integration option alongside anchor and pinocchio
• gates instruction-builder exports behind CPI/client features so native consumers can use quote verification/account parsing without pulling that surface
• makes libsecp256k1, spl-token, and spl-associated-token-account optional and enables them only from the existing client/CPI paths that need them
• enables bytemuck/derive for the existing bytemuck::Pod and bytemuck::Zeroable derives

Motivation

Native Solana programs that consume Switchboard quotes should not need to opt into Anchor, Pinocchio, client builders, CPI helpers, SPL token helper crates, or secp256k1 helper APIs just to use the on-chain quote verification path.

This keeps solana-v3 intact as a compatibility/version feature and introduces native as the integration flavor. devnet remains independent.

Validation

• cargo check --no-default-features --features native
• cargo check