fix: enforce strict < modulus for native byte conversions

[GarmashAlex]

Enforce documented strict inequality in BytesToNative() and () by introducing assertBytesLt and using it when WithAllowOverflow is not set.
Prevents accepting byte arrays equal to the field modulus, which previously allowed a non-unique representation of zero and could be exploited by malicious hints.Adds a negative test for the “bytes == modulus” case in BytesToNative().
Emulated conversions already enforced strictness; bringing native conversions into alignment with docs and intent.

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Note

Enforces strict less-than modulus in BytesToNative/NativeToBytes by extending assertBytesLeq with a disallowEquality flag and adds tests, while preserving overflow-allowed behavior.

• Conversion:
  • BytesToNative and NativeToBytes now enforce strict < modulus by calling assertBytesLeq(api, ..., field, true).
  • Extend assertBytesLeq to assertBytesLeq(api, b, bound, disallowEquality) to optionally forbid equality.
• Tests:
  • Add negative/positive cases where bytes equal the modulus (invalid without overflow; valid with WithAllowOverflow).
  • Update AssertBytesLeq circuit and test matrix to pass disallowEquality and validate both strict and non-strict comparisons.

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[ivokub]

Thanks for the PR! I refactored to have a single implementation with a switch and added a few tests.