refactor: optimize `pedersen` function

[nir11]

Description of the Changes

Replaced x = x.shrn(1) with x.iushrn(1) to perform an in-place unsigned right-shift operation. No new BN instances would be created for each shift operation.

Check List

• [x] Changes have been done against master branch, and PR does not conflict
• [ ] New unit / functional tests have been added (whenever applicable)
• [x] Test are passing in local environment
• [ ] Docs have been updated
• [x] PR title is follow the convention: <type>[optional scope]: <description>, e.g: fix: minor typos in code

[dan-ziv]

:tada: This PR is included in version 0.2.1-dev.2 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket:

[dan-ziv]

:tada: This PR is included in version 0.2.1 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket: