chore: make safeStringify static

Ticket: WP-6608

Author: danielpeng1

modules/sdk-core/src/bitgo/errors.ts

@@ -285,15 +285,15 @@ export class TxIntentMismatchError extends BitGoJsError {
     this.id = id;
     this.txParams = txParams;
     this.txHex = txHex;
-    this.txExplanation = txExplanation ? this.safeStringify(txExplanation) : undefined;
+    this.txExplanation = txExplanation ? TxIntentMismatchError.safeStringify(txExplanation) : undefined;
   }
 
   /**
    * Safely stringify a value with BigInt support
    * @param value - Value to stringify
    * @returns JSON string with BigInts converted to strings
    */
-  private safeStringify(value: unknown): string {
+  private static safeStringify(value: unknown): string {
     return JSON.stringify(value, (_, v) => (typeof v === 'bigint' ? v.toString() : v), 2);
   }