Grow StateArena across owner batches

[Lihi-AI]

Summary

This PR handles two related owner-side arena cleanups:

• move shared arena placement math (AlignOf, NormalizeArenaAlign) into common/app/scene/detail/ArenaMath.hpp
• let StateArena::reserve() append owner-lifetime blocks across multiple explicit state batches

Why

#56 gives shared arena arithmetic one small scene-detail home instead of making state code depend on Node.hpp.

#55 fixes the owner-level locality hole left after #29: later declareStates() batches can now reserve another arena block instead of falling back to heap merely because an earlier batch seeded the arena.

The growth boundary remains explicit:

• reserve() is the only operation that appends arena blocks
• allocate() consumes existing reserved capacity only
• owner-side immediate declarations reserve one slot before creation
• unreserved node-local state falls back to heap once existing capacity is exhausted, so detach can reclaim it

Validation

• cmake --build build/Testing
• cmake --build build/Testing-ASan
• ctest --test-dir build/Testing --output-on-failure -R LokaFlowDslTests
• ctest --test-dir build/Testing-ASan --output-on-failure -R LokaFlowDslTests

Red evidence for the review regression: before e9b6621, the new contract test failed because StateArena::allocate(1024, 4) appended a block after only reserve(32). After the fix, allocation returns 0 until an explicit reserve, and the owner path falls back to heap.

Notes

• #56: c0ec03e
• initial #55 implementation: e3b79a3
• review hardening: e9b6621
• block and raw-buffer allocation use std::nothrow under the no-exception policy

Closes #55
Closes #56

[Copilot]

Pull request overview

This PR centralizes shared arena placement/alignment math into a small scene-detail header and updates StateArena so owner-side state allocation can grow across multiple batches (instead of being effectively one-shot per owner), with a new contract test covering the multi-batch behavior.

Changes:

• Added common/app/scene/detail/ArenaMath.hpp and moved AlignOf / NormalizeArenaAlign usage to loka::app::scene::detail::*.
• Refactored StateArena to use chained blocks and allow allocate() to append new blocks when the current one is exhausted.
• Added a focused boundary/arena test that pins multi-batch owner locality and immediate state creation behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/BoundaryArenaTests.cpp	Adds a test owner + new contract test to verify StateArena grows across multiple owner batches and supports immediate state creation.
common/app/scene/state/StateBatchBase.hpp	Removes dependency on Node.hpp by using the new arena math header and detail:: alignment helpers.
common/app/scene/node/Conditional.cpp	Updates node alignment query to use detail::AlignOf.
common/app/scene/Node.hpp	Removes embedded arena math and includes detail/ArenaMath.hpp; updates node alignment to detail::AlignOf.
common/app/scene/detail/ArenaMath.hpp	New shared header providing AlignOf and NormalizeArenaAlign for arena sizing/allocation.
common/app/scene/composition/NodeComposition.cpp	Switches to detail/ArenaMath.hpp and detail::NormalizeArenaAlign for node arena sizing.
common/app/scene/boundary/detail/BoundaryArena.hpp	Implements growable StateArena via chained blocks; updates arena alignment normalization calls.
common/app/scene/boundary/Boundary.hpp	Always forwards reserve hints to StateArena (no longer gated on first-capacity).

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