feat: use-context-evaluation-with-newest-engine-version

[Zaimwa9]

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Closes #168

This PR upgrades the flagsmith-flag-engine from v6.1.0 to v10.0.3 following the approach from flagsmith-python-client#150, and implements the hide_disabled_flags project setting.

Changes

Engine Migration (v6 → v10)

• Upgraded flagsmith-flag-engine from 6.1.0 to 10.0.3
• Added flagsmith>=5 dependency for TypedDict models and mappers
• Migrated from Pydantic models to TypedDict-based evaluation contexts
• Replaced deprecated engine functions with new get_evaluation_result()
• Used map_environment_document_to_context() and map_context_and_identity_data_to_context() from flagsmith-python-client
• Updated traits handling from list[TraitModel] to dict[str, ContextValue] with backward compatibility validator
• Updated response mappers to work with new flag result format

hide_disabled_flags

• Added filter_disabled_flags() helper
• Implemented filtering in src/edge_proxy/environments.py for both /api/v1/flags/ and /api/v1/identities/ endpoints
• Only applies to client keys (server keys bypass this filter)
• Single feature requests return 404 if the feature is disabled and hide_disabled_flags == true

Tests

• Added new tests in tests/test_server.py for hide_disabled_flags functionality
• Added test fixture environment_with_hide_disabled_flags in tests/fixtures/response_data.py

How did you test this code?

Local Integration Testing:
1. Start edge proxy: rye run edge-proxy-serve
2. Test with Node.js SDK pointing to http://localhost:8000/api/v1/
3. Verify responses with hide_disabled_flags both enabled and disabled:

# Get all flags
curl -s -L -H "X-Environment-Key: ser.xxx" \
  http://localhost:8000/api/v1/flags/ | jq

# Get identity flags
curl -s -L -X POST \
  -H "X-Environment-Key: ser.xxx" \
  -H "Content-Type: application/json" \
  -d '{"identifier": "test-user"}' \
  http://localhost:8000/api/v1/identities/ | jq

[Zaimwa9]

I implemented hide_disabled_flags only for client keys. It's ambiguous in Project settings and it does mention that it's to hide the flags from end users.
Let me know if needs to do it for server keys too

[Zaimwa9]

This doesn't seem to be necessary anymore but would appreciate confirmation:

• this was used to have a cache access to server-side identity overrides
• engine now handles these overrides via the environment document
• it keeps the proxy stateless