Compilation Issue with serial Feature

[0xkanekiken]

While working on #321, I encountered a verification error that I believe is due to an unsatisfied AIR constraint.

Here's a screenshot of the error:

I found a section in the codebase that allows for the evaluation of all AIR constraints. This functionality is not enabled by default and is only turned on when compiling the codebase without the perf flag and disabling the default features.

sp1/core/src/stark/debug.rs

Lines 17 to 23 in 4cf6377

	pub fn debug_constraints<SC: StarkGenericConfig>(
	chip: &RiscvChip<SC>,
	preprocessed: Option<&RowMajorMatrix<SC::Val>>,
	main: &RowMajorMatrix<SC::Val>,
	perm: &RowMajorMatrix<SC::Challenge>,
	perm_challenges: &[SC::Challenge],
	) where

Attempting to compile the code with the serial feature (and default features turned off) resulted in compilation failure. This issue arises because the serial flag disables the rayon features, yet the module in question relies on rayon by default.

sp1/core/src/stark/permutation.rs

Lines 97 to 101 in 4cf6377

	// The permutation trace is actually the multiplicative inverse of the RLC's we computed above.
	permutation_trace_values
	.chunks_mut(chunk_rate)
	.par_bridge()
	.for_each(|chunk| batch_multiplicative_inverse_inplace(chunk));