Account for nested records

[matthijsr]

Previous RecordParser would successfully parse
INNER_NESTING_LEVEL 1
{ "key": { "key2": 1 } }

But fail on
INNER_NESTING_LEVEL 1
{ "key": { "key2": 1 }, "key3": { "key4": 1 } }

Completely skipping "key3" and anything beyond that.

The issue was that STATE_VALUE would check whether it was still nested:
(high downto 1) of the nesting register was 0
Then switch to STATE_IDLE as soon as it received a '}'.

In effect:

{ <- nesting reg: 01 (not nested)
"key":
{ <- nesting reg: 11 (is nested)
"key2": 1
}  <- nesting reg: 01 (not nested) -> STATE_VALUE ends the entire record
,
"key3": 
{
"key4": 1
}
}

This PR adds a number of tests against this behavior, and fixes the STATE_VALUE transition by also checking whether it is still inside the outer record (nesting reg: 01, otherwise 00).

It's possible nested arrays will produce the same issue in ArrayParser, but I haven't verified that yet.