[Feature] After configuring TabletPool Affinity, the Zone configuration will become invalid

Our Vitess will configure the following affinity, but this will cause the Zone to no longer take effect, causing the zone to not be as expected.

          tabletPools:
          - affinity:
              nodeAffinity:
                requiredDuringSchedulingIgnoredDuringExecution:
                  nodeSelectorTerms:
                  - matchExpressions:
                    - key: alpha.eksctl.io/nodegroup-name
                      operator: In
                      values:
                      - vitess-20
            cell: ap2d

The relevant code implementation is that after specifying any affinity, the default rule will no longer take effect.
Can we open nodeSelector or other methods/parameters to make custom affinity and zone configuration take effect at the same time?
https://github.com/planetscale/vitess-operator/blob/f36568a7ba67422adac8cc33cde4898d0b908294/pkg/operator/vttablet/pod.go#L359-L377

Reference: #604

Start by reproducing the YAML configuration and reading pkg/operator/vttablet/pod.go around lines 359-377, where the issue identifies the relevant implementation. Trace how custom affinity affects the default zone behavior, then verify that generated tablet pod scheduling configuration preserves both the requested affinity and zone settings.