Bump minimum Bazel version and add C++/Rust usage examples

[Subramanian-K812]

Add C++/Rust usage examples and bump minimum Bazel version to 8.6.0

Adds a runnable "getting started" example for test_scenarios_cpp/test_scenarios_rust, and
bumps the repo's minimum Bazel version.

What this PR does

1. Bazel version — bumps .bazelversion from 8.4.2 to 8.6.0
2. C++ example — score/test_scenarios_cpp/examples/basic.cpp, wired as a new cc_binary
   target (:basic) in score/test_scenarios_cpp/BUILD.
3. Rust example — score/test_scenarios_rust/examples/basic.rs, wired as a new
   rust_binary target (:basic) in score/test_scenarios_rust/BUILD.
4. Both examples implement two Scenarios (version.parse, version.satisfies_minimum)
   grouped under a nested version ScenarioGroup, demonstrating
   Scenario/ScenarioGroupImpl/TestContext/run_cli_app end to end.
   version.satisfies_minimum checks its input against this repo's own real minimum Bazel
   version (8.6.0), so success/failure is a genuine, real consequence of the input rather than
   scripted output.
5. A root examples/BUILD aliases both (//examples:cpp_basic, //examples:rust_basic) and
   examples/README.md documents them, following the same examples/ layout used by
   kyron and score_orchestrator.

Files

• .bazelversion — 8.4.2 → 8.6.0
• score/test_scenarios_cpp/examples/basic.cpp — new, C++ example
• score/test_scenarios_cpp/BUILD — adds the basic cc_binary target
• score/test_scenarios_rust/examples/basic.rs — new, Rust example
• score/test_scenarios_rust/BUILD — adds the basic rust_binary target
• examples/BUILD — new, root-level aliases (cpp_basic, rust_basic)
• examples/README.md — new, documents both examples

Verification

• bazel build //... / bazel test //... --config=x86_64-linux under Bazel 8.6.0 — unaffected,
  still pass (10 targets, 2/2 tests)
• bazel test --config=clang-tidy //score/test_scenarios_cpp:clang_tidy — passes (scope
  unchanged; doesn't cover examples/, same as tests/)
• cargo clippy --locked --all-targets -- -D warnings at pinned 1.92.0 — clean, 0 warnings
  (covers the new Rust example via --all-targets)
• ruff check . --exclude scripts/internal — all checks passed
• bazel test //:requirements_test — passes
• Both examples exercised directly for every documented command: --list-scenarios,
  --name version.parse --input 8.6.0, --name version.satisfies_minimum --input 8.6.0
  (success), --name version.satisfies_minimum --input 8.4.2 (genuine failure, exit 1),
  --name version.parse --input garbage (genuine parse failure, exit 1) — identical
  output/exit codes between C++ and Rust

Known limitations

• check_direct_dependencies now warns (non-fatal) for bazel_skylib, rules_cc, and
  buildifier_prebuilt, whose declared versions in MODULE.bazel are older than what's
  actually resolved — pre-existing drift surfaced by Bazel 8.6's stricter checking, not
  introduced by this change.
• The C++ example isn't covered by clang_tidy_test (that target's srcs only include the
  test_scenarios_cpp library, matching how tests/*.cpp is already excluded).

[PiotrKorkus]

combining bazel version as example is confusing for user. Do something unrelated to env, even simple enumeration would be good

[PiotrKorkus]

the whole point of scenarios is to use logging that comes with monotonic clock, same for cpp

[PiotrKorkus]

create a struct with Serialize/Deserialize, create a custom type instance by parsing input json. take a look at kyron tests implementation