Architecture + events refactor

[mickmaccallum]

• Refactors core Parra libraries to move away from singletons to improve predictability and testability.
• Unit tests are now reliable.
• Increases test coverage around core services.
• Starting work on HTTP metrics collection.
• Logging and error handling improvements.

• TODO comment audit
• Search for incomplete comment template strings
• Audit public access modifiers after refactor to single module
• Only publicly accessible types to have prefix "Parra"
• ! Can not ship with @_silgen_name linker override for backtrace calls.