fix: withdraw/deposit converts from BZZ (10^16 base units) (#66)

* refactor: added toBZZbaseUnit function

* feat: added utility for attesting value is BZZ convertible to base units

* fix: conversion from 15 to 16 decimal places, added unsafe versions

* refactor: withdraw modal uses the safe conversion from BZZ

* refactor: added BigNumber and Token class to handle BZZ digits correctly

* refactor: extract deposit and withdraw functionality into single modal

* test: added tests for Token

* chore: removed unused component

* chore: addressed PR review, token decimal is now integer 0-18

* chore: added comment to clarify the value restriction on token amount

src/utils/index.test.ts

@@ -0,0 +1,71 @@
+import BigNumber from 'bignumber.js'
+import { fromBZZbaseUnit, isInteger, makeBigNumber } from './index'
+
+describe('utils', () => {
+  describe('fromBZZbaseUnit', () => {
+    const values = [
+      { bzz: 0, baseUnits: 0 },
+      { bzz: 0.1, baseUnits: 1e15 },
+      { bzz: 0.9, baseUnits: 9e15 },
+    ]
+
+    values.forEach(({ bzz, baseUnits }) => {
+      test(`converting ${bzz} => ${baseUnits}`, () => {
+        expect(fromBZZbaseUnit(baseUnits)).toBe(bzz)
+      })
+    })
+  })
+
+  describe('isInteger', () => {
+    const correctValues = [
+      BigInt(0),
+      BigInt(1),
+      BigInt(-1),
+      new BigNumber('1'),
+      new BigNumber('0'),
+      new BigNumber('-1'),
+    ]
+    const wrongValues = ['1', new BigNumber('-0.1'), new BigNumber(NaN), new BigNumber(Infinity)]
+
+    correctValues.forEach(v => {
+      test(`testing ${v}`, () => {
+        expect(isInteger(v)).toBe(true)
+      })
+    })
+
+    wrongValues.forEach(v => {
+      test(`testing ${v}`, () => {
+        expect(isInteger(v)).toBe(false)
+      })
+    })
+  })
+
+  describe('makeBigNumber', () => {
+    const correctValues = [
+      BigInt(0),
+      BigInt(1),
+      BigInt(-1),
+      '1',
+      '0',
+      '-1',
+      '0.1',
+      new BigNumber('1'),
+      new BigNumber('0'),
+      new BigNumber('-1'),
+    ]
+    const wrongValues = [new Function(), 0, 1]
+
+    correctValues.forEach(v => {
+      test(`testing ${v}`, () => {
+        expect(BigNumber.isBigNumber(makeBigNumber(v))).toBe(true)
+      })
+    })
+
+    wrongValues.forEach(v => {
+      test(`testing ${v}`, () => {
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        expect(() => makeBigNumber((v as unknown) as any)).toThrow()
+      })
+    })
+  })
+})