Migrate to injectable warning features in score_bazel_cpp_toolchains

[4og]

What

Migrate Baselibs to the newest score_bazel_cpp_toolchains and use the injectable warning features introduced in score_cpp_policies#33 for the GCC and LLVM toolchains.

This centralizes warning policy configuration, keeps both toolchains aligned, and lets Baselibs benefit from shared policy updates.

Toolchain configuration

Inject selectable warning features with extra_known_features and default-enabled warning features with extra_enabled_features in each toolchain configuration.

Acceptance Criteria (DoD)

• Baselibs uses the newest compatible score_bazel_cpp_toolchains version.
• The GCC toolchain uses the injectable warning features from score_cpp_policies.
• The LLVM toolchain uses the injectable warning features from score_cpp_policies.

[ian-harmon-traton]

Created #524 to address this