Condenser for Browser Output Observations

[adityasoni9998]

End-user friendly description of the problem this fixes or functionality that this introduces

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  Developed a condenser that allows the user to only keep the most recent attention_window number of browser outputs in the LLM's context.

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Give a summary of what the PR does, explaining any non-trivial design decisions
Designed the BrowserOutputCondenser class for this functionality. This is helpful for long trajectories involving (possibly screenshot-based) web navigation to avoid context window exceeded errors and control inference cost. Previously implemented condensers do not allow masking a specific type of observation. Since, browser observations are generally very large, this might be helpful.

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Link of any specific issues this addresses