fix(ergo-explorer, ergo-node): fix vitest hangup

Because of a bug in vitest, it doesn't work correctly in multi-threaded
mode on some operating systems (only in some situations).

Disable threads to solve the issue.

Please note that the usage of `singleThread: true` in vitest config is
discouraged, as it runs all of the tests in the same environment, unlike
`threads: false` which runs each test in a child process.

Link to vitest issue (open at the time of commit):
vitest-dev/vitest#2008

packages/networks/ergo-explorer/vitest.config.ts

@@ -13,6 +13,7 @@ export default defineConfig({
     },
     mockReset: true,
     watch: false,
+    threads: false,
   },
   plugins: [wasm(), topLevelAwait()],
 });

packages/networks/ergo-node/vitest.config.ts

@@ -13,6 +13,7 @@ export default defineConfig({
     },
     mockReset: true,
     watch: false,
+    threads: false,
   },
   plugins: [wasm(), topLevelAwait()],
 });