fix(bandersnatch): GLV bounds + test

[yelhousni]

Description

When we revisited GLV scalar decomposition #213, we increased conditionally the loop bounds by 1 for all mulGLV methods for all curves but we forgot to do so for Bandersnatch twisted Edwards curve. This PR fixes the issue.

Type of change

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

How has this been tested?

added scalarMulWindowed which does a windowed double-and-add and compares the result with scalarMulGLV which uses the endomorphism. The method ScalarMultiplication picks scalarMulGLV whenever an efficient endomorphism is available (currently only for Bandersnatch).

How has this been benchmarked?

benchmark                          old ns/op     new ns/op     delta
BenchmarkScalarMulExtended-8       30378         30271         -0.35%
BenchmarkScalarMulProjective-8     33844         33941         +0.29%

No major diff for random scalars.

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

[yelhousni]

@ThomasPiellard this is just consolidating GLV in twisted Edwards with Weiestrass.

[ivokub]

LGTM