perf(emulated): small perf on doubleAndAdd

[yelhousni]

Description

smol perf that avoids some emulated subs.

Type of change

• New feature (non-breaking change which adds functionality)

How has this been tested?

All current related tests pass.

How has this been benchmarked?

Precompiles (scs):

• ECRECOVER:

old: 366 181
new: 365 153

• ECMUL:

old: 221 844
new: 221 280

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]

LGTM