Add cell name to assertion errors of APIs like assign_advice, assign_fixed, etc.

[ChihChengLiang]

In the halo2 assign_advice function, we can add a cell name as the function argument, as shown below.

region.assign_advice(|| "a", ...)

But that argument is never used in the function body.

Inside the function body, we have an assertion.:

halo2/halo2_proofs/src/dev.rs

Lines 457 to 463 in 73408a1

	assert!(
	self.usable_rows.contains(&row),
	"row={}, usable_rows={:?}, k={}",
	row,
	self.usable_rows,
	self.k,
	);

When the panic is triggered, the error message looks like below, it is hard to pin down the actual location of the root cause assignment.

panicked at 'row=131049, usable_rows=0..131049, k=17', .../halo2_proofs/src/dev.rs:494:9

A quick fix is to add the cell name to the panic string, so that the error message looks more helpful.

panicked at 'cell `a`, row=131049, usable_rows=0..131049, k=17', .../halo2_proofs/src/dev.rs:494:9

For a more ambitious goal, we can adopt the style written in this blog post https://mmapped.blog/posts/12-rust-error-handling.html#lift-input-validation. We can abstract the cell name, degree, column, row, and value as a new structure. We can define a validation error for this new struct, so that we no longer need input validation inside the assign_x function.