feat(refactor): Credentials.equal method and add unit tests

[DoctorLai]

What does this PR do?
Cleaner code and add unit test for Credentials.equal method

Why are these changes required?
Cleaner code and add unit tests

This PR has been tested by:

• Unit Tests
• Manual Testing

Follow up

Extra details

[codecov-commenter]

Codecov Report

Merging #3898 (3628b9c) into develop (e5c51ef) will increase coverage by 0.36%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             develop    #3898      +/-   ##
=============================================
+ Coverage      52.44%   52.80%   +0.36%     
- Complexity      7088     7148      +60     
=============================================
  Files            772      772              
  Lines          43410    43409       -1     
  Branches        4686     4684       -2     
=============================================
+ Hits           22766    22922     +156     
+ Misses         18820    18657     -163     
- Partials        1824     1830       +6     

Impacted Files	Coverage Δ
...k/src/main/java/org/tron/keystore/Credentials.java	57.14% <100.00%> (+57.14%)	⬆️
...mon/overlay/discover/table/DistanceComparator.java	80.00% <0.00%> (-20.00%)	⬇️
...rc/main/java/org/tron/core/vm/program/Program.java	60.29% <0.00%> (+0.09%)	⬆️
framework/src/main/java/org/tron/core/Wallet.java	17.02% <0.00%> (+0.22%)	⬆️
...java/org/tron/core/capsule/TransactionCapsule.java	51.69% <0.00%> (+0.24%)	⬆️
.../src/main/java/org/tron/core/db/KhaosDatabase.java	69.69% <0.00%> (+0.60%)	⬆️
.../java/org/tron/common/overlay/server/SyncPool.java	42.05% <0.00%> (+0.93%)	⬆️
.../main/java/org/tron/core/db2/common/TxCacheDB.java	71.60% <0.00%> (+1.23%)	⬆️
...mework/src/main/java/org/tron/core/db/Manager.java	58.68% <0.00%> (+1.61%)	⬆️
...va/org/tron/common/overlay/discover/node/Node.java	72.54% <0.00%> (+1.96%)	⬆️
... and 18 more

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