fix: fix sync on new blocks

[Keith-CY]

1. fix sync on new blocks. In the previous logic, registryOutPoint maps to a single model(https://github.com/ckb-js/kuai/pull/163/files#diff-6beced91eeabe7f90f6b66349a7a50e5a2e7cac2c73c536c6c32131c8082ddcdL21), which leads to that changes will only be sent to a single model instead of all models matched by the outPoint, so only one model will be updated(https://github.com/ckb-js/kuai/pull/163/files#diff-6beced91eeabe7f90f6b66349a7a50e5a2e7cac2c73c536c6c32131c8082ddcdL147) correctly. This PR maps registryOutPoint to a set of models to make sure they are all updated by the changes;
2. add a load method in the store model, which returns the global state combined from various cells matched in the store.