Clean up unsafe usages, tweak rust naming

[prasannavl]

Summary

• Aims to mark items that cross lang boundaries and require locking context as unsafe to get help from the compiler to avoid accidental usages on the Rust side, and unsure usage on the C++ side.

Based on: #2291

Implications

• Storage

  • Database reindex required
  • Database reindex optional
  • Database reindex not required
  • None

• Consensus

  • Network upgrade required
  • Includes backward compatible changes
  • Includes consensus workarounds
  • Includes consensus refactors
  • None