chore: strengthen backend eslint profile

src/integrations/tbank/decimal.spec.ts

@@ -21,3 +21,18 @@ describe('decimal', () => {
     ).toBe('1');
   });
 });
+
+describe('decimal formatting', () => {
+  it.each([
+    [120000n, 4, '12'],
+    [-120030n, 4, '-12.003'],
+    [1n, 4, '0.0001'],
+    [0n, 4, '0'],
+  ])('preserves value %s at scale %s while trimming only trailing zeros', (value, scale, expected) => {
+    expect(formatDecimal({ value, scale })).toBe(expected);
+  });
+  it('preserves a long fraction with a trailing zero run', () => {
+    const significant = '1'.repeat(10_000);
+    expect(formatDecimal({ value: BigInt(significant + '0'.repeat(10_000)), scale: 20_000 })).toBe('0.' + significant);
+  });
+});