Function isClmmPoolSeedIndexAvailable

Checks whether a CLMM pool already exists at the given seed index for this mint pair + amm config. Returns true when the index is free to use. Lamports donated to the pool address do not make it taken; only a created pool does (see isClmmPoolCreated). Throws when poolSeedIndex is outside 1..MAX_CLMM_POOL_SEED_INDEX (indices the program rejects).