chore(apps/playground-api): fix flakiness in WalletController.test.ts by using waitForExpect

[fuxingloh]

What this PR does / why we need it:

Add waitForExpect for wallet.listUnspent within WalletController.test.ts as it's known to be "flaky" from testing; wallet operations run differently on a separate wallet subsystem from blockchain core connectBlock, a block might get connected first before your wallet entries get indexed.

Which issue(s) does this PR fixes?:

Fixes part of #1771

[codeclimate]

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[codecov]

Codecov Report

Base: 92.19% // Head: 93.93% // Increases project coverage by +1.73% 🎉

Coverage data is based on head (31e6d41) compared to base (19011fd).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1999      +/-   ##
==========================================
+ Coverage   92.19%   93.93%   +1.73%     
==========================================
  Files         366      366              
  Lines       10985    10985              
  Branches     1432     1432              
==========================================
+ Hits        10128    10319     +191     
+ Misses        818      641     -177     
+ Partials       39       25      -14     

Impacted Files	Coverage Δ
...nsaction-builder/src/txn/txn_builder_masternode.ts	33.33% <0.00%> (-66.67%)	⬇️
...h-transaction-builder/src/txn/txn_builder_loans.ts	88.57% <0.00%> (-11.43%)	⬇️
packages/jellyfish-api-core/src/category/oracle.ts	91.42% <0.00%> (-8.58%)	⬇️
packages/jellyfish-transaction/src/tx_composer.ts	78.33% <0.00%> (-1.67%)	⬇️
packages/jellyfish-api-core/src/category/vault.ts	94.73% <0.00%> (ø)
...s/legacy-api/src/controllers/PoolPairController.ts	86.36% <0.00%> (+1.13%)	⬆️
...-api/src/module.indexer/model/dftx/active.price.ts	83.56% <0.00%> (+1.36%)	⬆️
packages/jellyfish-address/src/script/index.ts	100.00% <0.00%> (+2.04%)	⬆️
...nsaction-builder/src/txn/txn_builder_governance.ts	79.31% <0.00%> (+3.44%)	⬆️
packages/jellyfish-transaction/src/script/data.ts	81.63% <0.00%> (+6.12%)	⬆️
... and 20 more

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[github-actions]

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• ghcr.io/jellyfishsdk/playground-api:1244daed7335a0da7daabe23efaa74c7c5080975
• ghcr.io/jellyfishsdk/status-api:1244daed7335a0da7daabe23efaa74c7c5080975
• ghcr.io/jellyfishsdk/whale-api:1244daed7335a0da7daabe23efaa74c7c5080975