feat(pump): add buy_v2, sell_v2, buy_exact_quote_in_v2 instruction builders

Support Pump.fun Bonding Curve v2 unified trading interface with quote_mint
parameter for SOL-paired (WSOL) and USDC-paired coins.

- Add BUY_V2, SELL_V2, BUY_EXACT_QUOTE_IN_V2 discriminators
- Implement 27/26-account v2 instruction layouts matching official IDL
- Add PumpFunParams::quote_mint and use_v2_ix fields (default legacy)
- Add with_quote_mint() builder, buyback fee recipient pool, and PDA helpers
- Add v2 ix data encoders in pumpfun_ix_data.rs
- Legacy instructions remain default for backward compatibility

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/constants/accounts.rs

@@ -57,3 +57,9 @@ pub const RENT_META: solana_sdk::instruction::AccountMeta =
 
 pub const ASSOCIATED_TOKEN_PROGRAM_ID: Pubkey =
     pubkey!("ATokenGPvbdGVxr1b2hvZbsiqW5xWH25efTNsLJA8knL");
+pub const ASSOCIATED_TOKEN_PROGRAM_META: solana_sdk::instruction::AccountMeta =
+    solana_sdk::instruction::AccountMeta {
+        pubkey: ASSOCIATED_TOKEN_PROGRAM_ID,
+        is_signer: false,
+        is_writable: false,
+    };