feat: Implement Prometheus metrics exposure in SmartMetrics

- Added Prometheus gauges for CPU and memory metrics.
- Implemented HTTP server to expose metrics at /metrics endpoint.
- Created methods to enable and disable the Prometheus endpoint.
- Updated getMetrics() to set gauge values.
- Added tests for Prometheus metrics functionality.
- Updated documentation plan for Prometheus integration.

test/test.ts

@@ -1,6 +1,6 @@
 import * as plugins from './plugins.js';
 
-import { expect, tap } from '@push.rocks/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
 import * as smartmetrics from '../ts/index.js';
 
 let testSmartMetrics: smartmetrics.SmartMetrics;
@@ -24,4 +24,55 @@ tap.test('should produce valid metrics', async (tools) => {
   console.log(await testSmartMetrics.getMetrics());
 });
 
+tap.test('should return Prometheus formatted metrics', async () => {
+  const prometheusMetrics = await testSmartMetrics.getPrometheusFormattedMetrics();
+  expect(prometheusMetrics).toBeTypeofString();
+  expect(prometheusMetrics).toContain('smartmetrics_cpu_percentage');
+  expect(prometheusMetrics).toContain('smartmetrics_memory_percentage');
+  expect(prometheusMetrics).toContain('smartmetrics_memory_usage_bytes');
+  expect(prometheusMetrics).toContain('# HELP');
+  expect(prometheusMetrics).toContain('# TYPE');
+});
+
+tap.test('should enable Prometheus endpoint', async (tools) => {
+  const testPort = 19090;
+  testSmartMetrics.enablePrometheusEndpoint(testPort);
+  
+  // Give the server time to start
+  await tools.delayFor(1000);
+  
+  // Test the endpoint
+  const response = await fetch(`http://localhost:${testPort}/metrics`);
+  expect(response.status).toEqual(200);
+  expect(response.headers.get('content-type')).toEqual('text/plain; version=0.0.4');
+  
+  const metricsText = await response.text();
+  expect(metricsText).toContain('smartmetrics_cpu_percentage');
+  expect(metricsText).toContain('smartmetrics_memory_percentage');
+  expect(metricsText).toContain('smartmetrics_memory_usage_bytes');
+});
+
+tap.test('should handle 404 for non-metrics endpoints', async () => {
+  const response = await fetch('http://localhost:19090/notfound');
+  expect(response.status).toEqual(404);
+  const text = await response.text();
+  expect(text).toEqual('Not Found');
+});
+
+tap.test('should disable Prometheus endpoint', async () => {
+  testSmartMetrics.disablePrometheusEndpoint();
+  
+  // Give the server time to shut down
+  await new Promise(resolve => setTimeout(resolve, 1000));
+  
+  // Verify the endpoint is no longer accessible
+  try {
+    await fetch('http://localhost:19090/metrics');
+    throw new Error('Should have failed to connect');
+  } catch (error) {
+    // Expected to fail
+    expect(error.message).toContain('fetch failed');
+  }
+});
+
 tap.start();