Enhance coin retrieval logic in Iota client (#1472)

* Enhance coin retrieval logic in Iota client

- Introduced a constant `MINIMUM_BALANCE` to define the minimum balance required for transactions.
- Updated `get_coin_for_transaction` method to iterate through paginated coin data, selecting the coin with the highest balance that meets the minimum requirement.
- Improved error handling to provide clearer messages when no suitable coins are found.

This change optimizes the process of selecting coins for transactions, ensuring that only coins with sufficient balance are considered.

* chore: remove unecessary comments

* chore: simplify the coin logic

* chore: review comments

* Update identity_iota_core/src/rebased/client/full_client.rs

Co-authored-by: Enrico Marconi <31142849+UMR1352@users.noreply.github.com>

* Update minimum balance requirement in Iota client

---------

Co-authored-by: Enrico Marconi <31142849+UMR1352@users.noreply.github.com>

identity_iota_core/src/rebased/client/full_client.rs

@@ -10,6 +10,7 @@ use async_trait::async_trait;
 use fastcrypto::ed25519::Ed25519PublicKey;
 use fastcrypto::traits::ToFromBytes;
 use identity_verification::jwk::Jwk;
+use iota_sdk::rpc_types::Coin;
 use iota_sdk::rpc_types::IotaExecutionStatus;
 use iota_sdk::rpc_types::IotaObjectData;
 use iota_sdk::rpc_types::IotaObjectDataFilter;
@@ -47,6 +48,9 @@ use crate::rebased::Error;
 use super::get_object_id_from_did;
 use super::IdentityClientReadOnly;
 
+/// The minimum balance required to execute a transaction.
+pub(crate) const MINIMUM_BALANCE: u64 = 1_000_000_000;
+
 /// A signature which is used to sign transactions.
 pub struct IotaKeySignature {
   /// The public key of the signature.
@@ -253,18 +257,39 @@ impl<S> IdentityClient<S> {
     Ok(budget)
   }
 
-  async fn get_coin_for_transaction(&self) -> Result<iota_sdk::rpc_types::Coin, Error> {
-    let coins = self
-      .coin_read_api()
-      .get_coins(self.sender_address(), None, None, None)
-      .await
-      .map_err(|err| Error::GasIssue(format!("could not get coins; {err}")))?;
+  async fn get_coin_for_transaction(&self) -> Result<Coin, Error> {
+    const LIMIT: usize = 10;
+    let mut cursor = None;
+
+    loop {
+      let coins = self
+        .coin_read_api()
+        .get_coins(self.sender_address(), None, cursor, Some(LIMIT))
+        .await?;
+
+      let Some(coin) = coins.data.into_iter().max_by_key(|coin| coin.balance) else {
+        return Err(Error::GasIssue(format!(
+          "no coins found for address {}",
+          self.sender_address()
+        )));
+      };
+
+      if coin.balance >= MINIMUM_BALANCE {
+        return Ok(coin);
+      }
+
+      if !coins.has_next_page {
+        break;
+      }
+
+      cursor = coins.next_cursor;
+    }
 
-    coins
-      .data
-      .into_iter()
-      .next()
-      .ok_or_else(|| Error::GasIssue("could not find coins".to_string()))
+    Err(Error::GasIssue(format!(
+      "no coin found with minimum required balance of {} for address {}",
+      MINIMUM_BALANCE,
+      self.sender_address()
+    )))
   }
 
   async fn get_transaction_data(