Add support for openrouter

[gpsaggese]

In hopenai.py we want to add support for all models supported by openrouter by using the OpenAI interface

[gpsaggese]

I've started the work in #728 but didn't finish it

The next steps are:

• Generalize the code to use the openrouter interface
• Generalize the price counting interface
• Finish the notebook tutorial to show how the hopenai interface works
• Write a short document explaining the design principle of hopenai.py
• Compatible with the replay mechanism (there should be no change besides maybe storing the name of the model or some other metadata)

[gpsaggese]

• Also let's add a small script querying all the models

curl https://openrouter.ai/api/v1/models

and generating a CSV file with all the info about the models

Then we can use the code in the notebook (moved to hopenai) to extract info about the price

[gpsaggese]

Pls let's do multiple PR, one per bullet point so it's easy to review. You can organize the work as you want

[srinivassaitangudu]

@gpsaggese Please review the PRs
HelpersTask727_Generalise_hopenai.py_to_use_openrouter_interface
HelpersTask727_Querying_openrouter_models
HelpersTask727_Generalise_price_counting_interface_in_hopenai.py

[srinivassaitangudu]

[ ] Compatible with the replay mechanism (there should be no change besides maybe storing the name of the model or some other metadata)

A separate PR is not required for this. The openai.OpenAI() client returns responses in the same format as before, ensuring compatibility.

[gpsaggese]

Good work. I'll show you our flow to do stacked PR on Wed.

I believe what's left is only

• Finish the notebook tutorial to show how the hopenai interface works
• Write a short document explaining the design principle of hopenai.py

Pls confirm and mark the checkboxes done