chore: avoid nonnative dereferences

[ivokub]

Description

With the upcoming pr #749 it is necessary that we do not change the limb values of emulated.Element values. Mostly the API is designed in a way that this doesn't happen (we pass in and out pointers and do not perform in-place modifications), but there are a few cases in nonnative algebra where the API is overridden. This is mostly due to that for structs containing nonnative elements we need to use the value instead of pointer to count the number of field elements to allocate and have initialized values.

For example, if we have definition like:

type G1Affine struct {
    X, Y emulated.Element[emparams.BN254Fp]
}

and we compute

var P G1Affine
P = curve.Add(c.G, c.Q)
P.X = *emulated.Add(&p.X, other)

then we modify the value P.X. Now, as the multiplication checks are deferred for amortizing some computations, we get a failed check.

This PR changes such occurrences, making #749 more streamlined. Similar changes are already incorporated in #846.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How has this been tested?

• Rebased perf: non-native modular multiplication #749 on top and all tests are working.

How has this been benchmarked?

Not benchmarked, circuit stats are the same are the same.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[ivokub]

@gbotrel - pinging. This PR is a pre-requisite for #749.