Add docs-as-code documentation for test_scenarios

[Subramanian-K812]

Add docs-as-code documentation for test_scenarios and testing_utils

Adds a minimal docs-as-code setup covering both test_scenarios_cpp/test_scenarios_rust and testing_utils wired through score_docs_as_code.

What this PR does

1. docs/index.rst — a minimalistic general-concepts and usage doc: Scenario,
   ScenarioGroup/ScenarioGroupImpl, TestContext, and run_cli_app for the C++/Rust
   scenario libraries (pointing at the real basic examples), plus a short section on
   testing_utils's build-tool helpers, LogContainer, and ResultEntry.
2. docs/conf.py — Sphinx config matching kyron's current, CI-verified setup exactly,
   including score_metrics/sphinx_mounts/score_mounts (see Verification below for why
   these three specifically are required).
3. BUILD — wires the docs() macro over source_dir = "docs". The score_platform/
   score_process needs_json entries in data are left commented out, matching the one
   pattern already proven safe in kyron's live, currently-passing CI: those two are declared
   as dev_dependency in MODULE.bazel for future readiness but never actually referenced by
   any built target, so they stay invisible-but-harmless if this module is ever aggregated by
   another root module (e.g. reference_integration) that would otherwise lose visibility into
   dev_dependency-only deps.
4. MODULE.bazel — adds score_docs_as_code (regular dep, 8.0.1) and score_platform/
   score_process (dev deps, 0.7.1/1.5.4 — matching kyron's current pins).
5. .gitignore — adds /_build (root-level Sphinx artifact from bazel run //:docs/IDE
   tooling; not covered by the existing docs/_build/ rule), matching kyron's own fix for the
   identical artifact.
6. requirements.txt.lock — regenerated; the score_docs_as_code dependency chain bumps
   score_tooling transitively, which bumps one of its own pip pins (pygments).

Files

• docs/index.rst — new, documentation content
• docs/conf.py — new, Sphinx configuration
• BUILD — adds the docs() target
• MODULE.bazel — adds score_docs_as_code, score_platform, score_process
• .gitignore — adds /_build
• requirements.txt.lock — regenerated (transitive score_tooling bump)

Verification

• bazel build //... — clean, 30/30 targets, real metrics.json produced
• bazel test //... --config=x86_64-linux — 2/2 tests pass
• bazel test //:requirements.test — pass (after regenerating the lock file)
• bazel test --config=clang-tidy //score/test_scenarios_cpp:clang_tidy — pass
• cargo clippy --locked --all-targets -- -D warnings — clean, 0 warnings
• ruff check . --exclude scripts/internal — all checks passed

[PiotrKorkus]

add docs build and deploy in ci