Reset all cachedproperties in InflationSDP whenever generate_relaxation is called

[eliewolfe]

We use @cachedproperty decorators in both InflationLP and InflationSDP, but only the SDP requires called generate_relaxation to actually get going. As the cached properties depend on the relaxation, we really should wipe and reset them whenever generate_relaxation is called.
A further problem is that if the user calls a cached_property before running generate_relaxation, they will obtain a None (with error), but the value will not change from None upon calling generate_relaxation.