feat: Adds Tests + Decouples parseAmount fn + fix BigNumber inital parse

[moraesjeremias]

Description

• [x] Decouples parseAmount fn
• [x] Fix BigNumber inital parse (toFixed instead of toString)
• [x] Add test cases using node.js assert and test suite API (AAA pattern).

Related Issue

https://github.com/availproject/helm-values/issues

Motivation and Context

parseAmount fn can't handle scientific notated numbers, therefore it throws an error and returns an empty string. Must guarantee that all BigNumbers previously parsed will be strings not on scientific notation. As per BigNumber.js docs it's recommended toFixed instead of toString to avoid scientific notation.

How Has This Been Tested?

Github Actions Run #Test 2

Screenshots (if appropriate)