Confusion in constant-nonconstant branch of bigfield `assert_equal`

[codygunton]

@zac-williamson left a TODO saying "wtf" here. Someone should follow up with this.

[maramihali]

Interesting, I ran into the same problem with eccvm, I had to call self_reduce to make sure the non-constant value is not in the relaxed form because otherwise an assert equal that should be passing was failing. The assert equal was a check in sumcheck between a constant 0 and a non-constant 0