Feature add version namespace

[yuejiaointel]

This PR adds version namespace to allow backwards compatibility
design:

1. create a version header svs/version.hpp, define SVS_VERSION_NAMESPACE = v0, namespace svs { inline namespace v0 {} } (so users still use svs::Vamana)
2. wrap public api in version name space, example:
   SVS_VERSIONED_NAMESPACE_BEGIN
   class Vamana { ... };
   SVS_VERSIONED_NAMESPACE_END
3. faiss namespace svs_api = svs::v0, and switch versions later one without changing any intergration code