TapeAgents export for experiment results

[ollmer]

This PR introduces a simple compatibility layer for exporting traces of the BrowserGym experiments in a format compatible with the Tapes of the TapeAgents framework.
What does it do:

• convert a single trace of the experiment into a single Tape
• decomposes each StepInfo step of the experiment into 3 steps of the tape agents: observation, thought, and action.
• attempts to preserve as much metadata as possible for the step and for the whole trace.
• parses action in the simplest possible way as a string with a single Python function call
• if the think field is present in the agent info and not empty - it creates the thought step of the tape from it.
• method to save the tape in json format

The MVP is ready but not yet tested.

Next steps in this PR:

• test conversion over the real traces
• collect feedback from the BrowserGym team
• test tape loading on the TapeAgents side and rendering it with the tape browser

cc @recursix.

[ollmer]

I've simplified this PR down to <100 lines of changes in a single file and added support of tape_segments inside the agent_info, which could be produced by TapeAgent in the AgentLab.