feat: constant value binary decomposition

[ivokub]

Description

Handle binary decomposition for constant inputs.

Fixes #913. #1481 is duplicate of it, but it was not well implemented.

I also updated the test engine to mod-reduce the witness when copying. This mimics better the behaviour of actual solver.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How has this been tested?

• TestToBinaryConstantInput
• TestFromBinaryConstantInput
• TestFromBinaryInvalidInput

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]

Uh, ton of tests started to fail now. I'll see if there is something systematic.

[Copilot]

Pull Request Overview

This PR implements constant value binary decomposition and improves the handling of constant inputs in binary conversion routines, along with updating the test engine behavior for witness reduction.

• Improved witness reduction logic by mod reducing values when copying witness data.
• Enhanced binary conversion functions to separately handle constant inputs and added comprehensive tests for both valid and invalid cases.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/engine.go	Removed obsolete IsConstant and updated witness copying to mod reduce values.
std/math/bits/conversion_test.go	Added tests to validate binary conversion with constant inputs and ensured consistency between decomposed and constant binary representations.
std/math/bits/conversion_binary.go	Refactored handling of constant inputs in FromBinary and ToBinary; potential error in loop iteration in constant branch of ToBinary.
frontend/cs/scs/api_assertions.go	Refactored AssertIsLessOrEqual to use a switch for clarity and improved constant handling.
frontend/cs/r1cs/api_assertions.go	Similar refactoring as in scs assertions to handle constant bounds via a switch statement.

[ivokub]

Uh, ton of tests started to fail now. I'll see if there is something systematic.

Found the bugs. One was from my change and other one was another existing one.