remove read lock from ossl_method_store cache

[nhorman]

The query cache on every lookup takes a read lock, which despite being on the read side, still pollutes the cpu cache, as the read lock writes to the lock space to update the reader count. We can improve this by:

Replacing the method store cache with a series of atomically accessed linked lists
removing the read lock

[nhorman]

part of @mattcaswell work on openssl/openssl#30659 revealed that the ossl_method_store cache lock was taken on the read side very frequently, leading to performance degradation due to the cpu cache line pollution created by multiple threads attempting to frequently update the lock.

This work attempts to remove that lock from the cache add and lookup paths by converting the use of the internal hashtable on the method store to an atomic linked list.