fix: case-insensitive .dash suffix and UTXO double-spend prevention

- SDK: resolve_dpns_name() now handles ".DASH", ".Dash" etc. via
  eq_ignore_ascii_case (backport of dash-evo-tool PR #810 fix)
- platform-wallet: send_transaction() now calls check_core_transaction()
  after signing to mark spent UTXOs before broadcast, preventing
  concurrent callers from selecting the same inputs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lklimek

packages/rs-platform-wallet/src/wallet/core/wallet.rs

@@ -316,6 +316,17 @@ impl CoreWallet {
         self.sign_transaction_inputs(&secp, &mut tx, &selected_utxos)
             .await?;
 
+        // 5b. Mark spent UTXOs immediately while we can still prevent
+        // concurrent callers from selecting the same inputs.
+        {
+            use crate::wallet::platform_wallet_traits::WalletTransactionChecker;
+            use key_wallet::transaction_checking::TransactionContext;
+            let mut state = self.state.write().await;
+            state
+                .check_core_transaction(&tx, TransactionContext::Mempool, true, true)
+                .await;
+        }
+
         // 6. Broadcast.
         self.broadcast_transaction(&tx).await?;
 

packages/rs-sdk/src/platform/dpns_usernames/mod.rs

@@ -427,7 +427,7 @@ impl Sdk {
         let label = if let Some(dot_pos) = name.rfind('.') {
             let (label_part, suffix) = name.split_at(dot_pos);
             // Only strip the suffix if it's exactly ".dash"
-            if suffix == ".dash" {
+            if suffix.eq_ignore_ascii_case(".dash") {
                 label_part
             } else {
                 // If it's not ".dash", treat the whole thing as the label