refactor(scripts): implement ScriptContext

[glevco]

Motivation

Create the ScriptContext scaffolding that may be used by future opcodes.

Acceptance Criteria

• Create new, currently empty, ScriptContext class.
• Change function opcodes execution to use a new execute_op_code(), that takes a ScriptContext as an argument.
• Remove unused arguments from all opcode functions.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (cffe172) 85.34% compared to head (d3c075f) 85.25%.

Files	Patch %	Lines
hathor/transaction/scripts/opcode.py	97.08%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #851      +/-   ##
==========================================
- Coverage   85.34%   85.25%   -0.10%     
==========================================
  Files         281      282       +1     
  Lines       22392    22413      +21     
  Branches     3391     3402      +11     
==========================================
- Hits        19111    19108       -3     
- Misses       2599     2615      +16     
- Partials      682      690       +8     

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[jansegre]

Approved, but it's not a feature, it's a refactor, right?