refactor(encryption): add strict type hints to IEncryptionModule

[joshtrichards]

Summary

• Fully aligns IEncryptionModule interface and implementation function signatures
• Modernizes the interface (and its implementation) by introducing strict typing
• Drops redundant implementation docblocks (100% of essential API documentation now centralized in the interface)
• Helpful docblocks are added to non-interface helper functions for clarity and maintainability

Should be fully backwards compatible.

P.S. $position was already a de facto string. Any type related changes indicated in this PR for that parameter merely make it match implementation (and drop some casting). And despite it's name, it's used for string concatenation (at least in the context relevant to this PR).

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)