added pubkey bidirectional cache

[Fraccaman]

Issue Addressed

Closes #8783

Proposed Changes

This PR implements my understanding of how to fix the scenario described in #8783.
As described in the issue, this PR introduced a bidirectional cache between builder_index and public_key. It then leverage the new data structure to avoid the O(n) search.

Additional Info

• the only function Im seeing that modifies the length of the builder list is add_builder_to_registry. Here, a new builder is added to the list. My assumption is that the builder list 1) never shrinks 2) builders pubkeys never change. This means that the cache can only miss some entries from the builder list but will never have more entries that the builder list.

Let me know if the logic is wrong or if anything should be modified :)

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