feat(abstract-utxo): add protected isMainnet method

Add protected `isMainnet()` method to AbstractUtxoCoin class.
Default implementation delegates to `isMainnetCoin()` helper and
can be overridden by subclasses if needed.

Issue: BTC-0

Co-authored-by: llm-git <llm-git@ttll.de>

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -79,6 +79,7 @@ import {
   getFullNameFromCoinName,
   getMainnetCoinName,
   getNetworkFromCoinName,
+  isMainnetCoin,
   isUtxoCoinNameMainnet,
   UtxoCoinName,
   UtxoCoinNameMainnet,
@@ -409,6 +410,15 @@ export abstract class AbstractUtxoCoin
 {
   abstract name: UtxoCoinName;
 
+  /**
+   * Returns whether this coin is a mainnet coin.
+   * Default implementation uses the name property.
+   * Can be overridden by subclasses.
+   */
+  protected isMainnet(): boolean {
+    return isMainnetCoin(this.name);
+  }
+
   public readonly amountType: 'number' | 'bigint';
 
   protected readonly supportedTxFormats: { readonly psbt: boolean; readonly legacy: boolean } = {