feat: migrate testing framework to Bun and update test configurations

- Updated GitHub Actions workflow to use Bun's test runner and coverage reporting.
- Added comprehensive testing documentation for the Gitea Mirror project.
- Refactored test scripts in package.json to align with Bun's testing commands.
- Created new test files for database, Gitea, GitHub, health, and mirroring APIs.
- Implemented mock functions for API tests to handle various scenarios and responses.
- Established a test setup file for consistent test environment configuration.

src/lib/db/index.test.ts

@@ -0,0 +1,42 @@
+import { describe, test, expect, mock, beforeAll, afterAll } from "bun:test";
+import { drizzle } from "drizzle-orm/bun-sqlite";
+
+// Silence console logs during tests
+let originalConsoleLog: typeof console.log;
+
+beforeAll(() => {
+  // Save original console.log
+  originalConsoleLog = console.log;
+  // Replace with no-op function
+  console.log = () => {};
+});
+
+afterAll(() => {
+  // Restore original console.log
+  console.log = originalConsoleLog;
+});
+
+// Mock the database module
+mock.module("bun:sqlite", () => {
+  return {
+    Database: mock(function() {
+      return {
+        query: mock(() => ({
+          all: mock(() => []),
+          run: mock(() => ({}))
+        }))
+      };
+    })
+  };
+});
+
+// Mock the database tables
+describe("Database Schema", () => {
+  test("database connection can be created", async () => {
+    // Import the db from the module
+    const { db } = await import("./index");
+
+    // Check that db is defined
+    expect(db).toBeDefined();
+  });
+});