QVAC-8256: Enable MacOS dynamic backends

[jesusmb1995]

Dynamic back-ends on CI try to enable __ARM_FEATURE_SVE even though its not supported on MacOS (only linux). Therefore, add some additional guards. In addition, update common parse functions with an option to avoid calling load all backends, which leads to duplication when being called from multiple model instances.

Needed for:

• https://github.com/tetherto/qvac-registry-vcpkg/pull/64
• https://github.com/tetherto/qvac-lib-infer-llamacpp-embed/pull/118
• https://github.com/tetherto/qvac-lib-infer-llamacpp-llm/pull/341

Tests:

• Manually tested both Embeddings and LLM repo. Making sure it does pass tests.
• Embeddings repo CI: https://github.com/tetherto/qvac-lib-infer-llamacpp-embed/actions/runs/19704326792
• LLM repo CI: https://github.com/tetherto/qvac-lib-infer-llamacpp-llm/pull/341/checks

[jesusmb1995]

Test failing seems unrelated to this changes. Any iOS Device, error:iOS 26.1 is not installed.

[jesusmb1995]

Drafting this one for now. Since we might want to directly merge to 7048 version.