add new environment interface, add environment tests

[colinxs]

1. Signature changes:

• getreward -> getreward(state, action, observation, env)
• geteval -> geteval(state, action, observation, env)
• isdone -> isdone(state, action, observation, env)
  (the single argument versions (e.g. getreward(env)) is still defined for convenience, but internally calls getreward(getstate(env), getaction(env), getobservation(env), env)

2. Renames:

• AbstractEnv -> AbstractEnvironment
• observationspace(env) -> obsspace(env)
• evaluationspace(env) -> evalspace(env)
• all env_ctor arguments to env_tconstructor
• sharedmemory_envs(T, n, args...; kwargs...) -> tconstruct(T, n, args...; kwargs...)

3. Removals:

• NaieveEnvSampler (was primarily for debugging)
• effective_timestep(env) (leaving just timestep(env))
• reset!(env, state) and reset!(env, state, action)

4. Additions:

• setstate!(env, state) (replaces reset!(env, state))
• docstrings
• Some misc changes intended to address access to undefined reference in seed_threadrngs! #8
• Moves test_env from LyceumMuJoCo.jl to LyceumBase.jl and provides more comprehensive test coverage for environments.
• Misc improvements (e.g. more judicial use of @propagate_inbounds)