owasm: Refactor runtime code into owasm package

[sorawit]

Implementation details

This PR refactors owasm runtime code out to owasm package and let go-owasm only perform go-rust binding. This will allow standalone oracle script development environment based on rust in the future.

Please ensure the following requirements are met before submitting a pull request:

• The pull request is targeted against the correct target branch
• The pull request is linked to an issue with appropriate discussion and an accepted design OR is linked to a spec that describes the work.
• The pull request includes a description of the implementation/work done in detail.
• You have added a relevant changelog entry to CHANGELOG_UNRELEASED.md
• You have re-reviewed the files affected by the pull request (e.g. using the Files changed tab in the Github PR explorer)

[render]

Your Render PR Server URL is https://d3n-scan-pr-2339.onrender.com.

Follow its progress at https://dashboard.render.com/static/srv-bsh81qp8vr2amt5lo5p0.