Add support for BPF program custom errors (#5743)

* Add support for BPF program custom errors

* Rename SOL_SUCCESS -> SUCCESS

sdk/src/instruction.rs

@@ -70,6 +70,9 @@ pub enum InstructionError {
     /// CustomError allows on-chain programs to implement program-specific error types and see
     /// them returned by the Solana runtime. A CustomError may be any type that is represented
     /// as or serialized to a u32 integer.
+    ///
+    /// NOTE: u64 requires special serialization to avoid the loss of precision in JS clients and
+    /// so is not used for now.
     CustomError(u32),
 }