Invalid code generated for `Comparison` with missing parens

```python
from libcst import *

node = Comparison(
left=Name("a"),
comparisons=[
ComparisonTarget(
Equal(whitespace_before=ParenthesizedWhitespace(indent=True)),
Name("b"),
),
],
)

code = Module([]).code_for_node(node)
parse_module(code) # error, invalid syntax!
```

Related to #287 and #531; found via https://github.com/Zac-HD/shed/issues/84.

Start by running the provided Python reproduction and trace `Module([]).code_for_node` through `Comparison` serialization. Add a regression test for the missing-parentheses case, with completion defined as generated code that `parse_module` accepts without a syntax error.

Written by the indexing model from the issue text.