getMutableAllIncrementalRolloutFeatureFlags() stores pointers as const IncrementalRolloutFeatureFlag*, but findByName() needs to return a mutable pointer, requiring a const_cast. This pattern is backwards; we should store mutable and expose const, not store const and cast it away.

1. Change the internal vector to store non-const IncrementalRolloutFeatureFlag*
2. Change getAll() to return a reinterpret_cast const view
3. Remove const_cast in findByName()