Consider preventing vault state read when we're outside the pause window

[jubeira]

If we first check the timestamp, we don't need to read the vault state here: https://github.com/balancer/balancer-v3-monorepo/pull/644/files#diff-b757055907971a411ff87a80666c784ed52f185cd2cf892abbd46bfe9f1cd38dR157

[EndymionJkb]

I'm not sure what you mean here. _isVaultPaused is an &&, so if we're past the timestamp it will short-circuit and not check the vault state anyway (i.e., it already does check the timestamp first to avoid unnecessarily reading the VaultState).