Enhance concurrency strategy with traits, tests, and documentation

[FrozenLemonTee]

No description provided.

[Copilot]

Pull request overview

This PR updates the library’s concurrency strategy by replacing the previous atomic concurrency policy with a new fenced* family, extending the concurrency injection protocol to carry explicit memory orders, and adding primitive-level load/store/CAS support via concurrency handlers.

Changes:

• Replace policy::concurrency::atomic with policy::concurrency::{fenced, fenced_relaxed, fenced_acq_rel, fenced_seq_cst} and propagate memory-order-aware fence injection.
• Add primitive::load/store/compare_exchange implemented through the concurrency handler access protocol (backed by std::atomic_ref when supported).
• Update tests, examples, and README documentation to cover the new policies and access protocol.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/basic/test_policies.cpp	Adds coverage for new fenced policy traits, memory-order injection, and handler access availability gates.
tests/basic/test_operations.cpp	Renames/updates concurrency tests from atomic to fenced and adds load/store/CAS tests (incl. concurrent CAS increments).
src/primitive/impl.cppm	Adds concurrency-policy resolution/validation and introduces primitive atomic-access APIs via policy handlers.
src/policy/utility.cppm	Updates concurrency priority list to prefer fenced over none.
src/policy/impl.cppm	Defines new concurrency policy tags/traits and implements fenced handlers + std::atomic_ref-based access specializations.
src/policy/handler.cppm	Extends concurrency::injection with memory orders and introduces the handler access protocol/availability concepts.
src/operations/invoker.cppm	Threads the injected memory orders into runtime fence application.
examples/ex07_custom_policy.cpp	Updates custom concurrency handler example to set the new injection memory orders.
examples/ex05_concurrency_policy.cpp	Updates demo from atomic to fenced and showcases primitive load/store/CAS usage.
README.md	Documents new concurrency policy set and adds a concurrency access API example.