[Chore] Rename all on-chain/off-chain to onchain/offchain

[red-0ne]

Summary

Standardize the terminology used across the codebase and documentation by replacing instances of "on-chain" with "onchain" and "off-chain" with "offchain".

Issue

Type of change

Select one or more from the following:

• New feature, functionality or library
• Consensus breaking; add the consensus-breaking label if so. See [Infra] Automatically add the consensus-breaking label #791 for details
• Bug fix
• Code health or cleanup
• Documentation
• Other (specify)

Testing

• Unit Tests: make go_develop_and_test
• LocalNet E2E Tests: make test_e2e

Sanity Checklist

• I have tested my changes using the available tooling
• I have commented my code
• I have performed a self-review of my own code; both comments & source code
• I create and reference any new tickets, if applicable
• I have left TODOs throughout the codebase, if applicable