Added Connect4 Env wrapped on Gym

[VivekHaridas-01]

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[pankit-eng]

Please check if you would like to add this env docker image build to the github workflows.

[VivekHaridas-01]

Please check if you would like to add this env docker image build to the github workflows.

Hi @pankit-eng
I've replaced the previous connect4_env with a new, cleaner connect_four implementation — all files and logic have been rewritten.
This version includes updated server code, models, and documentation, aligned with the latest project conventions.
For now, I’ve kept the Docker image build out of the workflows to keep this PR focused.
Once this implementation is reviewed and merged, I can open a follow-up PR that adds the Docker image build to the GitHub workflows.

[Darktex]

Thank you for this contribution! Your code quality is excellent and shows good understanding of OpenSpiel.

However, we already have a generic OpenSpiel environment wrapper at src/envs/openspiel_env/ that supports 6 games (Catch, Tic-Tac-Toe, Kuhn Poker, Cliff Walking, 2048, Blackjack) and properly follows OpenEnv architectural patterns.

Your PR creates a separate connect_four environment that:

1. Uses different patterns (Pydantic models instead of OpenEnv base classes)
2. Duplicates the OpenSpiel integration approach
3. Would mean we have TWO ways to wrap OpenSpiel games in the codebase

This creates architectural inconsistency that we want to avoid in the reference examples we have here.

Compare your PR:

class ConnectFourAction(BaseModel):  # Pydantic
    column: int = Field(...)

... to the existing openspiel_env:

  @dataclass
  class OpenSpielAction(Action):  # Extends OpenEnv base class
      action_id: int

Incidentally, we also have #101 as another Connect4 environment but I don't think these two are conflicting: that is an implementation without OpenSpiel, and this is an OpenSpiel-based implementation. Both make sense to me.

Below is a copypasta of what Claude recommends to do if you want to make it available via OpenSpiel:

If you'd like to make Connect4 available via OpenSpiel, the right approach would be to:

1. Add "connect_four" to the supported games list in src/envs/openspiel_env/
2. Update the README with Connect4-specific documentation
3. Follow the existing patterns (see how Tic-Tac-Toe is implemented)

This would give users a choice:

• Simple Connect4: PR #101 (custom, lightweight)
• OpenSpiel Connect4: via openspiel_env (research-grade, works with OpenSpiel algorithms)

Let us know if you'd like to pursue the OpenSpiel integration approach! We'd welcome that contribution to openspiel_env.