Tx pool tests

[MakisChristou]

@libotony It was easier for me to create a new PR from scratch. I added your suggestions refactoring the NewDevnet function to take a timestamp argument instead of duplicating it. I also used the CreateTemp function in our test cases as you suggested. Code coverage is above 80% in this PR.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (869e9c5) 53.89% compared to head (1b2c195) 54.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #636      +/-   ##
==========================================
+ Coverage   53.89%   54.73%   +0.83%     
==========================================
  Files         179      179              
  Lines       20665    20665              
==========================================
+ Hits        11138    11311     +173     
+ Misses       8703     8522     -181     
- Partials      824      832       +8     

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[MakisChristou]

By the way regarding the empty lines its probably cause by go fmt since its running every time I save on VS Code

[libotony]

By the way regarding the empty lines its probably cause by go fmt since its running every time I save on VS Code

I am also using vscode plus go language plugin, it does not add new lines of every new function but accepts one empty line.

[libotony]

BTW, the tests are failing since math/big is missing in txpool_test.go