Load all the info before showing a list of found CIS-2 tokens

[Radiokot]

Purpose

This is a second part of more lenient CIS-2 Lookup.

Changes

• Load token metadata and balances before showing the list of found tokens
• Filter out tokens with corrupted or missing metadata
• Show "This contract has no valid tokens" if all the contract tokens are invalid
• Get rid of token lookup errors made obsolete by this change (invalid index, invalid metadata, invalid metadata checksum)

Internally:

• Use new fail-proof batch endpoints to fetch metadata and balance info

Checklist

• [x] My code follows the style of this project.
• [x] The code compiles without warnings.
• [x] I have performed a self-review of the changes.
• [x] I have documented my code, in particular the intent of the hard-to-understand areas.
• [x] (If necessary) I have updated the CHANGELOG.

[github-actions[bot]]

File	Coverage [0%]	:x:
ProxyRepository.kt	0%	:x:
TokensViewModel.kt	0%	:x:
ContractAddressFragment.kt	0%	:x:
ProxyBackend.kt	0%	:x:

Total Project Coverage	1.01%	:x:

[Radiokot]

Yesterday Aleš quickly created new fail-proof CIS2 batch endpoints for balances and metadata, I'm about to use them to speed up the loading.

[github-actions[bot]]

File	Coverage [0%]	:x:
ProxyRepository.kt	0%	:x:
TokensViewModel.kt	0%	:x:
ContractAddressFragment.kt	0%	:x:
ProxyBackend.kt	0%	:x:

Total Project Coverage	1.01%	:x: