Remove unused interfaces and types

[Jack-Khuu]

As titled. Specifically removed:

• interfaces.py: Environment, Policy
• types.py: ForgeEnvInfo, Action, Trajectory, State

Also test_replay_buffer was updated to use a locally defined TestEpisode instead of a Trajectory since the test was the only caller of Trajectory (and was using it more as a proxy for Episode due to the definition not being centralized)

---

python -m pytest tests/unit_tests/test_replay_buffer.py::TestReplayBuffer

[Jack-Khuu]

Failing on deleted env tests: Will be rebased onto and landed after #443

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.48%. Comparing base (248126a) to head (3b89a92).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #446      +/-   ##
==========================================
- Coverage   63.57%   63.48%   -0.09%     
==========================================
  Files          77       77              
  Lines        7569     7526      -43     
==========================================
- Hits         4812     4778      -34     
+ Misses       2757     2748       -9     

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