refactor: isBlockNumber

[ghost]

Description

This PR uses isBlockNumber() to remove redundancy.

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 #405 (c3794be) into dev (96c014e) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head c3794be differs from pull request most recent head f80809a. Consider uploading reports for the commit f80809a to get more accurate results

@@            Coverage Diff             @@
##              dev     #405      +/-   ##
==========================================
- Coverage   81.28%   81.27%   -0.02%     
==========================================
  Files          43       43              
  Lines        1811     1810       -1     
  Branches      334      332       -2     
==========================================
- Hits         1472     1471       -1     
  Misses        338      338              
  Partials        1        1              

Impacted Files	Coverage Δ
packages/zilliqa-js-blockchain/src/chain.ts	66.83% <100.00%> (-0.17%)	⬇️

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