Consolidate key logic into fewer locations

[mhess-swl]

Background

There are numerous places in the codebase where logic for handling Ed25519 and Secp256k1 (ECDSA) keys. This ticket represents a refactoring effort to consolidate said logic into fewer locations, both so 1) the logic isn't as difficult to find and 2) we reduce duplication.

Acceptance Criteria

1. Common key logic is refactored into fewer places
2. Logic specific to key types (Ed25519, Secp256k1) is separated from common key logic
3. Key reads and writes for both key types use the same (read/write) algorithms

Keys are fundamental throughout our unit and hapi test suites, so ensuring that existing tests all pass should be sufficient to verify correctness.

Dependencies

None

Definition of Ready (DoR) Checklist

• Clear acceptance criteria
• Clear and detailed description
• Dependencies identified
• Links to documentation
• Should be completable in 2-3 Days
• Initial draft of Low-level design document
• At least high level test plan
• Groomed/Estimated

Definition of Done (DoD) Checklist

• Acceptance Criteria complete
• No Codacy issues greater than minor (in new code)
• JavaDocs updated/created
• Code commented
• Unit tests created/updated
• 80% test code coverage (in new code)
• Happy Path and major negative cases in HAPI tests as applicable