fix(explorer): avoid holdings state updates during render

[umeeSthein]

### motivation

The holdings view in the address route was mutating local state during render.

It reset holdings pagination and the show-all toggle when the address changed, and it also clamped the current holdings page during render when the visible asset count shrank. That makes the route fragile and can cause unnecessary rerenders or pagination flicker when holdings data changes asynchronously.

### implications

- move holdings reset-on-address-change into React.useEffect

- move holdings page clamping into React.useEffect

- render address transitions with the default holdings UI state immediately

- reuse the normalized holdings page count for both row slicing and the holdings footer