Json serialization poc

[cameron-devine]

PR: Upgrade to C++23, Replace oatpp with cpp-httplib, Add Glaze JSON Serialization

Summary

Upgrades tsflib from C++17/20 to C++23 to support the Glaze high-performance JSON serialization library. As part of this modernization effort, the heavyweight oatpp HTTP framework (which has ceased active development) has been replaced with the lightweight, header-only cpp-httplib.

Motivation

• oatpp is unmaintained — the project has stopped receiving updates on GitHub, making it a liability as a dependency.
• Glaze offers compile-time, reflection-based JSON serialization that is significantly faster than nlohmann and works reliably across compiled library boundaries (unlike cereal, which suffered from static registration issues when linking across .a units).
• C++23 is required by Glaze and positions the codebase for a future C++26 upgrade, which will enable even cleaner reflection-based serialization without explicit metadata templates.

Changes

Dependency changes:

• ❌ Removed oatpp (HTTP framework + HTTP client)
• ✅ Added cpp-httplib — lightweight, header-only HTTP client (pulled from Conan)
• ✅ Added glaze 7.2.0 — compile-time JSON serialization (pulled from Conan)

HTTP client migration:

• Replaced all oatpp API client calls (InfluxDB adapter, etc.) with httplib::Client
• Removed unused oatpp DTO files and request/response wrappers
• Enabled automatic path encoding via httplib::Client::set_path_encode(true) for proper URL handling of special characters

Glaze integration:

• Added glz::meta template specialization for TSF::Clock using glz::custom accessors for getter/setter-based properties (name, period, offset)
• Updated SqliteStore CRUD methods and RtxJsonUtilities archive/unarchive to use Glaze serialization for Clock objects
• Updated unit tests to validate round-trip serialization via glz::write_json / glz::read_json

Build configuration:

• Set CXX_STANDARD 23 in CMakeLists.txt
• Updated conanfile.py with new dependencies

Future Work

• C++26: Once AppleClang supports C++26, the explicit glz::meta template specializations can be eliminated entirely in favor of inline compile-time reflection, removing boilerplate from data classes like Clock.
• nlohmann_json removal: Glaze could fully replace nlohmann throughout the project. Currently nlohmann is still used in areas like InfluxDB response parsing and the REST service layer — these can be migrated incrementally.
• Expand Glaze to additional data classes: The pattern established with Clock can be applied to other tsflib types (TimeSeries, Units, Curve, etc.) for consistent cross-library serialization.

Testing

• All clock serialization tests updated and passing
• Round-trip (serialize → deserialize) validation for default values, custom values, and edge cases
• InfluxDB adapter HTTP calls verified with cpp-httplib