[feature] Support @solana/kit (web3.js 2.x) types in Solana adapter

[PaulRBerg]

What problem does this new feature solve?

The Solana adapter currently uses @solana/web3.js 1.x types (PublicKey class, Transaction/VersionedTransaction classes). Modern Solana libraries are migrating to @solana/kit (web3.js 2.x), which uses:

• Address - branded string type from @solana/addresses
• Transaction & TransactionWithLifetime - functional transaction types from @solana/transactions

This creates type incompatibility when integrating AppKit with Effect-TS based Solana libraries or other modern tooling built on the 2.x SDK.

Specific pain points:

1. publicKey: PublicKey cannot be assigned to publicKey: Address without manual conversion
2. signTransaction<T extends AnyTransaction> uses legacy types, incompatible with <T extends Transaction & TransactionWithLifetime>
3. No clean way to bridge between the two type systems

Describe the solution you'd like

Add support for @solana/kit types alongside the existing @solana/web3.js types. Options:

1. Dual exports: Provide both legacy and modern typed interfaces

   // Existing
   export interface Provider {
     publicKey?: PublicKey;
     signTransaction<T extends AnyTransaction>(tx: T): Promise<T>;
   }
   
   // New
   export interface ModernProvider {
     publicKey: Address | null;
     signTransaction<T extends Transaction & TransactionWithLifetime>(tx: T): Promise<T>;
   }

2. Conversion utilities: Export helpers to convert between SDK generations

   export function toModernAddress(pk: PublicKey): Address;
   export function toLegacyPublicKey(addr: Address): PublicKey;

3. Full migration to @solana/kit with backwards compatibility shims

The Solana ecosystem is gradually moving to 2.x - supporting it now would future-proof AppKit for this transition.

[linear]

REOWN-4367