EVM: Benchmarks: define dependencies versions

Context

Contributes to #6091 (closed)

The benchmark scripts don't define their dependencies. This MR changes that by adding a package.json definition. Scripts now only need a npm install to run, no dependencies to fetch by hand.

Manually testing the MR

cd src/kernel_evm/benchmarks
npm install

Shouldn't output errors.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR