Add 'neotest.ReadNEF' method

[Chubru]

Close #3679

Problem

Currently, neotest lacks functionality to load compiled contracts. This feature would be useful for testing migrations between different contract versions.

Solution

Add LoadContract method to load a contract from a NEF file.

While implementing this, I used contractDeploy as a reference.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.

Project coverage is 83.08%. Comparing base (6d20772) to head (0362359).

Files with missing lines	Patch %	Lines
pkg/neotest/compile.go	0.00%	24 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3771   +/-   ##
=======================================
  Coverage   83.08%   83.08%           
=======================================
  Files         335      335           
  Lines       46745    46769   +24     
=======================================
+ Hits        38836    38860   +24     
+ Misses       6320     6314    -6     
- Partials     1589     1595    +6     

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