Migrate collection and category queries to data layer

[bard]

Fixes: #2749

Depends on: #2731

Description

Core:

• move collection and category queries to the data layer
• make queries async so as to be independent from where they come from (source or remote service)

Additional:

• (optional, experimental): allow fetching collections from a Google spreadsheet (example). Enable with:

new DataLayer({ 
  collections: { googleSheetsUrl: 'https://docs.google.com/...' }
})

• cleared console/test warnings

Testing

In the PR environment, browse collections and categories and compare with corresponding collections/categories in production. Results should be the same (minus shuffling of entries). Edit: collections and categories are no longer visible after merging latest main, but they can still be verified in the deployment for the previous commit (at least as long as Vercel keeps it around): https://explorer-6d4mfl1jy-grants-stack.vercel.app/

Checklist

This PR:

• Includes only changes relevant to the original ticket. Significant refactoring needs to be separated. Does not apply — the change is the refactoring.
• Doesn't disable eslint rules.
• Doesn't work around the type checker (including but not limited to: type casts, non-null assertions, @ts-ignore, unjustified optional values).
• Doesn't contain commented out code.
• If adding/updating a feature, it adds/updates its test script on Notion.

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[melissa-neira]

lgtm!

[gitstream-cm]

This PR is 51.41760818588787% new code.