refactor: add more SIMD into OAHSet

[BorysTheDev]

No description provided.

[qodo-free-for-open-source-projects]

Review Summary by Qodo

Refactor OAHSet SIMD operations into separate implementation file

✨ Enhancement 🧪 Tests

Walkthroughs

Description

• Extracted inline SIMD probe logic from oah_set.h into separate oah_set.cc implementation file
  with FORCE_INLINE annotations for better code organization and maintainability
• Refactored core search operations (ProbeLanes, FindMatch, RefreshStaleCandidate,
  ProbeExtensionVector) into dedicated helper functions with clearer separation of concerns
• Simplified public API methods (Add, Find, Erase, AddMany) by moving implementation details
  to private helper functions while maintaining performance through forced inlining
• Added comprehensive stress test (SimdFindEraseStress) covering displacement window, extension
  vectors, lazy-zero hash cache, TTL expiry, and mixed live/erased/expired member resolution
• Enhanced SimdOp class with constexpr and noexcept qualifiers for compile-time evaluation
  support

[qodo-free-for-open-source-projects]

Code Review by Qodo

🐞 Bugs (1) 📘 Rule violations (0)

1. Public internal SIMD API 🐞 Bug ⚙ Maintainability

Description

OAHSet::LaneMasks and the template OAHSet::ProbeLanes are declared in the class public section even
though they are internal implementation details. This unnecessarily expands the public API and
leaves a publicly-declared template whose definition lives only in oah_set.cc, making accidental
external use/refactors riskier.

Code

src/core/oah_set.h[R167-179]

Evidence

The header exposes LaneMasks and declares the ProbeLanes template in the public section, while
the only definition is in the new .cc file and all current uses are within that TU. This indicates
they are internal implementation details and should not be part of the public interface.

src/core/oah_set.h[152-186]
src/core/oah_set.cc[18-27]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

### Issue description
`LaneMasks` and `ProbeLanes` are internal probing helpers but are currently in `OAHSet`'s public API. This exposes implementation details and creates a publicly-declared template whose definition is only available in `oah_set.cc`.

### Issue Context
These helpers are only used by the new SIMD probing implementation in `oah_set.cc` and are not intended as part of the `OAHSet` external interface.

### Fix Focus Areas
- src/core/oah_set.h[167-186]
- src/core/oah_set.cc[18-27]

### What to change
- Move `struct LaneMasks` and `template <typename Wide> static LaneMasks ProbeLanes(...)` into the `private:` section of `OAHSet`, or alternatively keep them as `private` static helpers.
- If you expect future reuse outside the TU, move the template definition to the header (and keep it `private`) to avoid accidental ODR/visibility surprises.

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---

[augmentcode]

🤖 Augment PR Summary

Summary: Refactors OAHSet to push more of the hot-path probing logic into SIMD-based scans for both the displacement window and the extension vector.

Changes:

• Moves `OAHSet` hot-path logic (`Add`, `AddMany`, `Find`, `Erase`) out of the header into a new implementation file: src/core/oah_set.cc
• Introduces SIMD helpers (ProbeLanes, lane masks) and consolidates shared lookup logic via FindMatch/FindInternal
• Adds refresh logic for lazy/stale extended-hash candidates during probing
• Updates the build to compile the new TU (src/core/CMakeLists.txt)
• Adds a stress test covering SIMD find/erase across window/vector paths and TTL expiry (SimdFindEraseStress)
• Tightens `SimdOp` APIs with more constexpr/noexcept qualifiers

Technical Notes: The new probe path uses SIMD masks to shortlist key-compare candidates (including lazy-zero hash lanes) and applies expiry during probe to keep lookups/erases consistent.

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[augmentcode]

Review completed. 2 suggestions posted.

Comment augment review to trigger a new review at any time.

[augmentcode]

SimdOp::Load is now declared constexpr but it calls std::memcpy, which is not usable in constant evaluation in C++20 and can make the function definition ill-formed depending on the standard/library implementation. If this project is still built as C++20, this may break compilation (or at least makes the constexpr promise incorrect).

Severity: high

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[augmentcode]

LaneMasks/ProbeLanes look like internal helpers, but they currently live in the class public section, and ProbeLanes is a template only declared in the header (definition is in oah_set.cc). If any other TU ever tries to use it, it will fail to compile/link; consider keeping these helpers private (or fully header-defined) to avoid exposing a fragile API surface.

Severity: low

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