Several fixes for misbehaving NFTGrid

[modersohn]

Follow-up for #195 after discovering several issue

• remove unused PageSize parameter
• follow top-down parameter rule, a component should never change it's own parameters, that is always the task of the parent
  • use _internalPage for binding to MudPagination
  • that way we can make it happy, by setting it directly in gotoPage to avoid it switching back and forth
• we need PageNumber and the NFTSlots to reliably load the metadata
  • but any and each parameter change will tricker OnParameterSetAsync
  • to determine when we're actually ready to load a new NFTdata collection we need to store for what page and slots we loaded last
  • this requires that AccountDetails and NFTCollection pages never use empty NFTSlots as intermediary, because the NFTGrid has no way of knowing whether this is the real slots
• cts should also be disposed in Dispose, if present

[modersohn]

Well, silly me thought I'd learned so much about writing Blazor components after #195 but there's been numerous issue with that. Essentially a component should never change its own [Parameter] and you basically get OnParameterSetAsync call for each one, maybe even more and even if it didn't actually change. Which makes it very tricky to decide when to actually try to load the NFT data here and when to cancel previously running loads.

I'd appreciate if you could give this a proper look but almost more importantly a proper test drive (maybe even after the merge on dev deployment?). Switching pages with/without interrupting it, but also hiding the NFTGrid by switching to balances (because then it'll get released!), also checking out collections. There were so many issues, it's not very likely I caught them all.

[modersohn]

I'll merge this into dev for now, so testing can happen on the dev deployment