Improve NFT listing performance

[rynoV]

Resolves #11

• [x] Batch datum fetching
  • See https://github.com/mlabs-haskell/seabug-contracts/pull/12/commits/37aa71b7bac7c5b5a21b5b242d9ace447eb3f05f
• [x] Parellelize metadata fetching
  • See https://github.com/mlabs-haskell/seabug-contracts/pull/12/commits/46b6ff23d8b6dfa8c12010c5b0273140778f42d6
• [x] Need to consider that the blockfrost api rate limiting might be hit
  • If we're just doing a POC with <500 images it should be fine for now
  • Added some basic handling, but if we get to the point of hitting the limitting we should probably refactor to use something like pagination
  • See https://github.com/mlabs-haskell/seabug-contracts/pull/12/commits/dabfb1bb21051aed90a9da7cded24008b81a4580
• [x] Remove unnecessary double parsing of blockfrost responses
  • See https://github.com/mlabs-haskell/seabug-contracts/pull/12/commits/3a18d29cf5b524699ba6590c56789fa8fdaec714
• [x] Test: same NFTs shown on page in same order (no regression)
• [x] Speed up utxo fetching
  • Moved to #14
• [x] Don't list all NFTs for the individual item pages
  • Update: listing all NFTs only happens when the item page is opened directly (not through the home page), or it is reloaded
  • See #16
• [x] Implement pagination
  • Moved to #15

Times to load page:

• Original time to show images: ~55 seconds
• After batching datum fetching: ~40 seconds
• After parallelizing metadata fetching + batching datum fetching: ~20 seconds
  • Today (July 7th) utxosAt was faster, only ~5 seconds, page load was ~10 seconds
  • Today (July 8th) utxosAt was back to ~15 seconds