feat: Add support for hooks.

[kinyoklion]

There are two primary aspects to this PR. The first is support for hooks, and the second is support for a Go context like addition to the variation API.

The reason for this addition is that it may not be possible in all environments to automatically get the current span parent using OTEL.

The default context management strategy in OTEL uses thread-local storage, which can cause problems when an async framework is handling multiple requests in a single thread. In that scenario the application manually determines the parent-child relationship (unless they have async aware custom context management).

BEGIN_COMMIT_OVERRIDE
feat: Add support for hooks.
fix: Discard track events when the associated context is invalid.
END_COMMIT_OVERRIDE

---

Note

Introduce a full hooks system (with hook context) across C++ and C APIs, integrate it into evaluations/tracking, add WithHookContext overloads, drop invalid-context track events, and update build/deps with extensive tests.

• Hooks framework (C++ core):
  • Add hooks::Hook, HookContext, EvaluationSeriesContext/Data(+Builder), TrackSeriesContext and hook_executor for before/after evaluation and after track.
  • Wire hooks into ClientImpl variation/track paths with method names; execute hooks synchronously.
  • Extend Config/ConfigBuilder to accept std::shared_ptr<hooks::Hook> list.
• C++ API:
  • Add Track and all *Variation* overloads accepting hooks::HookContext.
• C bindings:
  • New headers/APIs: hook.h, hook_context.h, evaluation_series_context.h, evaluation_series_data.h, track_series_context.h.
  • Register hooks via LDServerConfigBuilder_Hooks; bridge via CHookWrapper.
  • Add *_WithHookContext functions for track and all variation variants.
• Events behavior:
  • Discard track events when Context is invalid; log warning.
• Build/Deps:
  • Include new hook sources in CMakeLists.txt.
  • Update redis-plus-plus FetchContent tag and disable shallow clone.
• Tests:
  • Add comprehensive C++ and C binding tests for hook ordering, data passing, error handling, and contexts.

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[kinyoklion]

bugbot review

[kinyoklion]

So, there was a mistake with the syntax of the clang-tidy suppression in the base binding implementations. Which result in suppressing all tidy messages.

We are not doing that here, and the result is that these opaque struct definitions were encountering: https://clang.llvm.org/extra/clang-tidy/checks/bugprone/reserved-identifier.html

Which isn't going to be a problem because the compiler isn't going to spontaneously reserve these very specific names.

But to appease it here I have started with p_. This first name isn't used by calling code, but we just want it to not look like it should be used either.