Rtgym

- Removes the busy loop when `rtgym` waits for a new observation, using a `threading.Event` instead
- Improves benchmarking, adding the option to record time tracess of `rtgym` internal calls instead of Polyak averages

Newer versions of Gymnasium require that the users call custom APIs in `env.unwrapped`. This applies to the `wait` API in `rtgym`. This change introduced a bug in the `benchmark.py`, which is now fixed.

Thread-safe implementation of Real-Time Gym.

Highlights:
- Version `0.13` introduces a new implementation of Real-Time Gym: `"real-time-gym-ts-v1"`. This new implementation relies on signaling via `threading.Event`, which enables `rtgym` to run a single persistent thread in the background (whereas `"real-time-gym-v1"` is spawning and joining a new thread at each time-step). This vastly improves `rtgym`'s thread-safety, but may require careful handling, as waiting for an `Event` that never comes (e.g., because of a crash) may cause your program to hang.
- `"real_time"` and `"async_threading"` were removed from the configuration dictionary, as the behavior for their non-default values was never implemented anyway.

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Added 3 advanced API functions that allow changing the time-wise configuration of `rtgym` environments on-the-fly:
- `set_time_step_duration`
- `set_start_obs_capture`
- `set_ep_max_length`

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Minor optimizations.

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This version fixes a couple minor bugs related to reset transitions.

In particular, it introduces the `set_default_action` API, and a new entry in the configuration dictionary to chose whether `reset` should send the default action or the last action of the previous episode.

A thorough sanity check has been added in the `tests` folder.