[CHIA-689] Port test_nft_offers.py to WalletTestFramework

[Quexington]

Another PR migrating our wallet tests to the paradigmatic WalletTestFramework. As has been the case for recent PRs, no wallet changes were needed, this is purely a test change.

[coveralls-official]

Pull Request Test Coverage Report for Build 13314238807

Details

• 176 of 176 (100.0%) changed or added relevant lines in 1 file are covered.
• 14 unchanged lines in 5 files lost coverage.
• Overall coverage increased (+0.01%) to 91.516%

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Files with Coverage Reduction	New Missed Lines	%
chia/full_node/pending_tx_cache.py	1	96.55%
chia/daemon/server.py	1	83.46%
chia/rpc/rpc_server.py	4	88.24%
chia/wallet/wallet_node.py	4	87.96%
chia/_tests/core/util/test_lockfile.py	4	88.43%

Totals
Change from base Build 13291657602:	0.01%
Covered Lines:	105071
Relevant Lines:	114634

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💛 - Coveralls