fix: concat buffer bug

[charles-cooper]

What I did

fix #3737

How I did it

How to verify it

Commit message

the `concat()` builtin did not respect the `copy_bytes()` API, it
allocated a buffer in some cases which did not have enough padding.

patches GHSA-2q8v-3gqq-4f8p

Description for the changelog

Cute Animal Picture

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (56b0d4f) 84.78% compared to head (80f409e) 84.58%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3738      +/-   ##
==========================================
- Coverage   84.78%   84.58%   -0.20%     
==========================================
  Files          92       92              
  Lines       13137    13139       +2     
  Branches     2929     2929              
==========================================
- Hits        11138    11114      -24     
- Misses       1535     1560      +25     
- Partials      464      465       +1     

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[cyberthirst]

can we also add the other PoCs and assert c.foo() == -1? tested different paths

# GHSA-2q8v-3gqq-4f8p
code = """
s: String[1]
s2: String[33]
s3: String[34]

@external
def __init__():
    self.s = "a"
    self.s2 = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" # 33*'a'

@internal
def bar() -> uint256:
    self.s3 = concat(self.s, self.s2)
    return 1

@external
def foo() -> int256:
    i: int256 = -1
    b: uint256 = self.bar()
    return i
"""

# GHSA-2q8v-3gqq-4f8p
code = """
i: immutable(int256)

@external
def __init__():
    i = -1
    s: String[2] = concat("a", "b")

@external
def foo() -> int256:
    return i
"""

[charles-cooper]

see 80f409e and 50b50cd