perf: contract storage optimisation

[shreyasbhat0]

Closes #559 Closes #574

Checklist:

• [x] I have performed a self-review of my own code
• [ ] I have documented my code in accordance with the documentation guidelines
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have run the unit tests
• [x] I only have one commit (if not, squash them into one commit).
• [ ] I have a descriptive commit message that adheres to the commit message guidelines

Please review the CONTRIBUTING.md file for detailed contributing guidelines.

[codecov[bot]]

Codecov Report

Merging #773 (c333426) into main (4dbf564) will increase coverage by 0.04%. The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #773      +/-   ##
============================================
+ Coverage     38.02%   38.07%   +0.04%     
  Complexity      801      801              
============================================
  Files           115      115              
  Lines         11152    11152              
  Branches        941      941              
============================================
+ Hits           4241     4246       +5     
+ Misses         6590     6585       -5     
  Partials        321      321              

Impacted Files	Coverage Δ
cmd/iconbridge/chain/bsc/receiver.go	59.02% <0.00%> (+1.21%)	:arrow_up: