feat: Add HTML test page for formatting functions

- Introduce a new HTML file that tests various formatting utility functions, including number, Satoshi, millisatoshi, currency, event price, and wallet balance formatting.
- Implement a structured layout with sections for each test type and a summary of test results.
- Include JavaScript to run tests on page load, displaying success and error results for each formatting function.
- Update import paths in the existing TypeScript test file to ensure compatibility with the new structure.

src/lib/utils/formatting.test.ts

@@ -10,7 +10,7 @@ import {
   formatCurrency, 
   formatEventPrice, 
   formatWalletBalance 
-} from './formatting'
+} from './formatting.js'
 
 // Test data
 const testNumbers = [