Env-scoped lru cache.

[chenkins]

Description
LRU cache is global, and not local to a RailEnv. Cache is reset in multiple places by calling send_infrastructure_data_change_signal_to_reset_lru_cache(). However, some cached function calls use @lru_cache directly - these cached calls are not reset by send_infrastructure_data_change_signal_to_reset_lru_cache(), although some of these functions cache env-specific data.

Two steps:

1. send_infrastructure_data_change_signal_to_reset_lru_cache() must reset all LRU caches (or at least all LRU caches with env-specific data).
2. major refactoring to make LRU caching local to a RailEnv and (if possible) reduce the number of locations where cache reset is called.

Relates to #92 .

To Reproduce
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Expected behavior
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Information
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• OS: [e.g. Mac]
• Python version [e.g. 3.8]
• Package version [e.g. 3.0.15]

Additional context
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