feat: add method to validate feature toggles

[NicoleMGomes]

Disclaimer: Do not include SAP-internal or customer-specific information in this PR (e.g. internal system URLs, customer names, tenant IDs, or confidential configurations). This is a public repository.

Description

Adds feature toggle support to the runtime context module. DWCContextProvider now reads the dwc-stage-configuration request header — a base64-encoded JSON payload listing feature flags with their enabled state — and exposes the names of all enabled toggles as the new FEATURE_TOGGLES context key (ContextKey[List[str]]). A new top-level helper is_feature_enabled(name) checks whether a named toggle is active for the current request, returning False when the header is absent, malformed, or the toggle is not enabled.

Related Issue

Closes #

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Dependency update

How to Test

1. Bootstrap an application with bootstrap(app) (uses DWCContextProvider by default).
2. Send a request with header dwc-stage-configuration: <base64-encoded JSON> where the JSON has the shape {"features":[{"name":"MY_FEATURE","enabled":true}]}.
3. Inside a request handler, call is_feature_enabled("my-feature") — expect True.
4. Call is_feature_enabled("absent-feature") — expect False.
5. Send a request without the header; both calls return False.
6. Run unit tests: pytest tests/core/unit/runtime_context/ -v — all 45 tests pass.

Checklist

• I have read the Contributing Guidelines
• I have verified that my changes solve the issue
• I have added/updated automated tests to cover my changes
• All tests pass locally
• I have verified that my code follows the Code Guidelines
• I have updated documentation (if applicable)
• I have added type hints for all public APIs
• My code does not contain sensitive information (credentials, tokens, etc.)
• I have followed Conventional Commits for commit messages

Additional Notes

• FEATURE_TOGGLES is exported from sap_cloud_sdk.core.runtime_context alongside the existing DWC keys.
• is_feature_enabled is also exported at the same level for ergonomic use in request handlers.
• Whitespace around individual toggle names in the header value is trimmed.