refactor(sae): unify time functions in VM config and hooks

See: https://github.com/ava-labs/avalanchego/blob/7fc1fe66b9c10f8032c866ba2bd6157306f28abd/vms/saevm/sae/vm_test.go#L266

Tests need to set the same mock clock in both `vmConfig.Now` and `vmConfig.Hooks.Now`. Easy to forget one.

Could have hooks derive their time from the VM config's `Now` function, or have a single source of truth that both read from.

Start with vms/saevm/sae/vm_test.go around line 266 and inspect how the test configures vmConfig.Now and vmConfig.Hooks.Now. Trace the VM config and hooks time entry points to determine where the duplicate clock values are introduced. Done means tests need one mock-clock source while both VM configuration and hooks observe the same time.

Written by the indexing model from the issue text.