Tool-based actions, env as a tools collection

[ollmer]

This PR is a prerequisite for switching the Gaia agent from the simple browser to the Browsergym (i.e., the full Chromium browser).

1. introduces base classes for a tool (consumes action, produces observation) and multitool (has an inner state and can consume multiple different actions)
2. provides universal caching of the tool results
3. converts search, code executor, calculator old and new browser into new tools/multitools
4. redefines gaia environment as a collection of tools, new env can route actions accordingly
5. removes outdated prompts and step types
6. stores actions in the relevant tools modules and makes them available for any agent, not just gaia.
7. slightly updated logic of multithreaded locks, should produce less congestion