feat(pumpswap): align pool account and events with cashback IDL

- Extend on-chain Pool layout (is_cashback_coin, 7-byte reserved, 244 bytes)
  with backward-compatible decode for 236-byte legacy accounts
- Decode Buy/Sell program logs manually: min_base_amount_out, ix_name,
  cashback fields; optional sell cashback when payload >= 368 bytes
- Set ix_name on buy / buy_exact_quote_in instructions; merge new fields
  in CPI log merger
- Add read_i64_le helper and pool layout unit test

Made-with: Cursor

src/streaming/event_parser/common/utils.rs

@@ -24,6 +24,15 @@ pub fn extract_program_log<'a>(log: &'a str, prefix: &str) -> Option<&'a str> {
     log.strip_prefix(prefix)
 }
 
+/// 安全地从字节数组中读取 i64
+pub fn read_i64_le(data: &[u8], offset: usize) -> Option<i64> {
+    if data.len() < offset + 8 {
+        return None;
+    }
+    let bytes: [u8; 8] = data[offset..offset + 8].try_into().ok()?;
+    Some(i64::from_le_bytes(bytes))
+}
+
 /// 安全地从字节数组中读取u64
 pub fn read_u64_le(data: &[u8], offset: usize) -> Option<u64> {
     if data.len() < offset + 8 {