Add walker for values

[turbolent]

Work towards #870

Description

Add a function to walk an interpreter.Value, WalkValue, similar to ast.Walk.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #1037 (b3f5e1e) into master (ffe9881) will decrease coverage by 0.01%.
The diff coverage is 55.17%.

@@            Coverage Diff             @@
##           master    #1037      +/-   ##
==========================================
- Coverage   75.55%   75.53%   -0.02%     
==========================================
  Files         268      270       +2     
  Lines       32999    33028      +29     
==========================================
+ Hits        24932    24948      +16     
- Misses       6944     6956      +12     
- Partials     1123     1124       +1     

Flag	Coverage Δ
unittests	75.53% <55.17%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/interpreter/block.go	65.71% <0.00%> (-8.48%)	⬇️
runtime/interpreter/deployed_contract.go	28.57% <0.00%> (-3.43%)	⬇️
runtime/interpreter/function.go	56.00% <ø> (ø)
runtime/interpreter/walk.go	66.66% <66.66%> (ø)
runtime/interpreter/inspect.go	75.00% <75.00%> (ø)
runtime/interpreter/value.go	77.49% <75.00%> (-0.01%)	⬇️

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[SupunS]

Nice!