fix: refine stacktrace attribution of errors thrown from middleware (#21470)

* Refine middleware types to include the method signature and to express the nullability of the middleware.

* Make sure that the stacktrace does not involve middleware unless the error originated from the middleware itself.

Co-authored-by: steveluscher <github@steveluscher.com>

web3.js/test/connection.test.ts

@@ -133,6 +133,35 @@ describe('Connection', () => {
     });
   }
 
+  it('should attribute middleware fatals to the middleware', async () => {
+    let connection = new Connection(url, {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      fetchMiddleware: (_url, _options, _fetch) => {
+        throw new Error('This middleware experienced a fatal error');
+      },
+    });
+    const error = await expect(connection.getVersion()).to.be.rejectedWith(
+      'This middleware experienced a fatal error',
+    );
+    expect(error)
+      .to.be.an.instanceOf(Error)
+      .and.to.have.property('stack')
+      .that.include('fetchMiddleware');
+  });
+
+  it('should not attribute fetch errors to the middleware', async () => {
+    let connection = new Connection(url, {
+      fetchMiddleware: (url, _options, fetch) => {
+        fetch(url, 'An `Object` was expected here; this is a `TypeError`.');
+      },
+    });
+    const error = await expect(connection.getVersion()).to.be.rejected;
+    expect(error)
+      .to.be.an.instanceOf(Error)
+      .and.to.have.property('stack')
+      .that.does.not.include('fetchMiddleware');
+  });
+
   it('get account info - not found', async () => {
     const account = Keypair.generate();