fix(rules_score): stop duplicating feature requirements in component docs

[simon-d-bmw]

Summary

component() lists feature_requirements alongside component_requirements in its requirements attribute so the feature requirement's .lobster file is available to resolve derived_from references from the component requirements. component.bzl's Sphinx-doc collection loop did not distinguish between the two providers, so every component listing a feature_requirements target re-rendered that feature's full requirements page into its own docs — duplicating the feature requirements content once per referencing component, plus once at the dependable_element level (which already renders it correctly from its own requirements attribute).

Changes:

• private/component.bzl: only collect SphinxSourcesInfo.srcs from ComponentRequirementsInfo-providing targets in requirements; FeatureRequirementsInfo targets remain usable there for Lobster tracing but no longer contribute rendered RST to the component's own docs. Docstring updated to document this.
• test/unit_component_test.bzl / test/BUILD: add component_excludes_feature_req_docs_test, asserting a component's SphinxSourcesInfo.srcs contains its own component_requirements RST but not a co-listed feature_requirements RST.

Validation: bazel test //... (from bazel/rules/rules_score/test/, a separate module) — 64/64 tests pass, including the new regression test.