[FEATURE] Continuous Actions PPO

[OmaymaMahjoub]

Feature

Enhance PPO systems by introducing support for continuous actions

Proposal

Two implementation approaches are considered:

1. Create a select_actions file containing both discrete and continuous action selections, and integrate this into the single-file PPO systems.
2. Split the existing ff_ippo file into two separate files: one for discrete actions and another for continuous actions.

Mandatory checklist before making a PR

• [x] Implement continuous actions network and function
• [x] Make all the different PPO architecture support the continous actions (rec/ff) (IL/CTDE)
• [x] Benchmarking on MaBrax or a different jax environment that support continoues actions

Links/references

• Current branch feat/continuous_actions.