feat[test]: add code writing DSL to test suite

[charles-cooper]

What I did

this makes it easier to programmatically generate vyper source code, which will make it easier to write parametrized tests in the test suite.

How I did it

How to verify it

Commit message

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Description for the changelog

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.00%. Comparing base (812d903) to head (fc7d4ef).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4691      +/-   ##
==========================================
+ Coverage   92.99%   93.00%   +0.01%     
==========================================
  Files         131      131              
  Lines       19094    19095       +1     
  Branches     3324     3324              
==========================================
+ Hits        17757    17760       +3     
+ Misses        899      898       -1     
+ Partials      438      437       -1     

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[cyberthirst]

vars will be public by default?

[cyberthirst]

why does the visibility for constants differ?

[cyberthirst]

for immutables we don't have to declare with "immutable" but for constants "constant" is required?

[cyberthirst]

the model seems to be missing features like pragmas, interfaces, module-related machinery (imports, initialization,..)

[cyberthirst]

looks reasonable overall, for parametric tests it could be an improvement over status quo

for simple tests, it's a bit hard to read

code = """
owner: address

@deploy
def __init__(initial_count: uint256):
    self.count = initial_count
    self.owner = msg.sender

@external
def increment():
    self.count += 1

@external
@view
def get_count() -> uint256:
    return self.count
 """"

vs

    model = CodeModel()

   count = model.storage_var("count: uint256")
   owner = model.storage_var("owner: address")

   code = (
       model.function("__init__(initial_count: uint256)")
       .deploy()
       .body(
           f"""
           {count} = initial_count
           {owner} = msg.sender
       """
       )
       .done()
       .function("increment()")
       .external()
       .body(f"{count} += 1")
       .done()
       .function("get_count() -> uint256")
       .external()
       .view()
       .body(f"return {count}")
       .done()
       .build()
   )