refactor: no hardcoding

[ghost]

Description

This PR replaces 'GetBalance' with RPCMethod.GetBalance.

Motivation and Context

How has this been tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• Add tests to cover changes as needed.
• Update documentation as needed.

[codecov-commenter]

Codecov Report

Merging #340 (63d9c75) into dev (c054901) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 63d9c75 differs from pull request most recent head 8cb52d5. Consider uploading reports for the commit 8cb52d5 to get more accurate results

@@           Coverage Diff           @@
##              dev     #340   +/-   ##
=======================================
  Coverage   80.58%   80.58%           
=======================================
  Files          44       44           
  Lines        1787     1787           
  Branches      299      299           
=======================================
  Hits         1440     1440           
  Misses        346      346           
  Partials        1        1           

Impacted Files	Coverage Δ
packages/zilliqa-js-account/src/wallet.ts	82.17% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c054901...8cb52d5. Read the comment docs.