Unwanted newlines being added to output.

Start with the provided Python reproducer and trace how tomlkit serializes tables after nested tables are added. Compare the round-trip and changed outputs, then add a regression test covering the newline behavior; done means table spacing follows the explicitly constructed structure without surprising extra newlines.

I want to group my tables:

[first]
foo = 5
bar = 20
[first.a.b.c]
alice = 10
bob = 30

[second]       
foo = 3
bar = 21
[second.a.b.c]
alice = 15
bob = 3543

When I try to manually construct this, I instead get

[first]
foo = 5
bar = 20

[first.a.b.c]
alice = 10
bob = 30


[second]       
foo = 3
bar = 21

[second.a.b.c]
alice = 15
bob = 3543

I expected no newlines to be added for me and explicitly called out a newline between [first.a.b.c] table and [second]. Newlines being added surprised me and made made me wonder if tomlkit was properly preserving the lack of newlines but it seems to.

So I created the following test case to experiment with how newlines are dealt with

import tomlkit

t = tomlkit.loads("""[first]
foo = 5
bar = 20
[first.a.b.c]
alice = 10
bob = 30
[second]
foo = 3
bar = 21
[second.a.b.c]
alice = 15
bob = 3543""")

print("Round-trip")
print("```toml")
print(tomlkit.dumps(t))
print("```")
print()

t["second"].add("extra", tomlkit.table())
t["second"].add("extra1", tomlkit.table())
three = tomlkit.table()
three["foo"] = 2
three["bar"] = 1
child = tomlkit.table()
child["alice"] = 3
child["bob"] = 10
three["child"] = child
t["three"] = three


print("Changed")
print("```toml")
print(tomlkit.dumps(t))
print("```")
print()

The output is:
Round-trip

[first]
foo = 5
bar = 20
[first.a.b.c]
alice = 10
bob = 30
[second]
foo = 3
bar = 21
[second.a.b.c]
alice = 15
bob = 3543

Changed

[first]
foo = 5
bar = 20
[first.a.b.c]
alice = 10
bob = 30
[second]
foo = 3
bar = 21
[second.a.b.c]
alice = 15
bob = 3543
[second.extra]

[second.extra1]

[three]
foo = 2
bar = 1

[three.child]
alice = 3
bob = 10

I was surprised that second.extra didn't have a newline before it but second.extra1 did. I imagine this just shows how the newlines are being auto-added but it is still surprising.