test: Add unit tests for ExecutionResult constructors

[axic]

Either coverage is wrong, or the explicit constructor is not called. With these tests we make sure that values are always correct even if in the case Trap/Void don't get assigned via the explicit constructor, but by setting the trapped variable. We can figure out the case with coverage later (cc @chfast).

[codecov]

Codecov Report

Merging #435 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #435   +/-   ##
=======================================
  Coverage   99.32%   99.33%           
=======================================
  Files          50       50           
  Lines       14075    14107   +32     
=======================================
+ Hits        13980    14013   +33     
+ Misses         95       94    -1     

[gumb0]

Do you want to try to cover the constexpr constructor line? I think this might do it

bool success = false; // non const variable
const ExecutionResult result{success};
EXPECT_FALSE(result.trapped);

[gumb0]

Maybe it would execute the constructor with this being const, too, I'm not sure, just thought with non-const it's less probable to be optimized away.
Can be merged like this, anyway.

[axic]

const ExecutionResult result{1234};

results in

/Users/alex/Projects/fizzy/test/unittests/api_test.cpp:46:27: error: call to constructor of 'const fizzy::ExecutionResult' is ambiguous
    const ExecutionResult result{1234};
                          ^     ~~~~~~
/Users/alex/Projects/fizzy/lib/fizzy/execute.hpp:25:15: note: candidate constructor
    constexpr ExecutionResult(uint64_t _value) noexcept : has_value{true}, value{_value} {}
              ^
/Users/alex/Projects/fizzy/lib/fizzy/execute.hpp:29:24: note: candidate constructor
    constexpr explicit ExecutionResult(bool success) noexcept : trapped{!success} {}
                       ^
/Users/alex/Projects/fizzy/lib/fizzy/execute.hpp:18:8: note: candidate constructor (the implicit move constructor)
struct ExecutionResult
       ^
/Users/alex/Projects/fizzy/lib/fizzy/execute.hpp:18:8: note: candidate constructor (the implicit copy constructor)