Improve inference in space constructors

[charleskawczynski]

In particular, I'm seeing a bunch of jet failures in warpedspace of test/Spaces/terrain_warp.jl. We should probably add more systematic tests, as this can improve compile times.

[charleskawczynski]

It turns out that a big culprit here is the OBJECT_CACHE, which is inherently type stable since it takes a type-unbounded dict.

IMO, this is not really the correct way to test if two spaces are compatible (and won't generally work, even for the coupler). Removing the get!-OBJECT_CACHE logic from all the constructors fixes a huge number of type instabilities, ironically speeding up the construction of the space. Subsequent calls can be faster, but I'm wondering if this is worth it