[VM Benchmark] benchmark convert

[Jim8y]

Description

StackItem convert has alwasys being one of the most expensive operation in the vm, thus having this pr to benchmark the convert function.

This is part of the plan to fully study the neo-vm performanace and prepare to optimize the performance bottleneck.

More benchmark targeting various other neo vm methods will come later.

Fixes # None

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Test Configuration:

Checklist:

• My code follows the style guidelines of this project
• 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
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules