fix: operation simulation route in x/nft test

[julienrbrt]

Description

#12233 introduced a mistake in the NFT operation test.

• This PR fixes it and ensure we check the operation errors in all tests, so mistakes like this cannot happen.
• Removes the last bit of simapp from NFT and move helpers to testutil/sims

---

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• confirmed the correct type prefix in the PR title
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[codecov]

Codecov Report

Merging #12278 (0b2992b) into main (c68fa3b) will decrease coverage by 0.02%.
The diff coverage is 85.18%.

@@            Coverage Diff             @@
##             main   #12278      +/-   ##
==========================================
- Coverage   66.12%   66.10%   -0.03%     
==========================================
  Files         710      675      -35     
  Lines       74175    71280    -2895     
==========================================
- Hits        49048    47118    -1930     
+ Misses      22216    21518     -698     
+ Partials     2911     2644     -267     

Impacted Files	Coverage Δ
simapp/test_helpers.go	15.38% <0.00%> (ø)
simapp/utils.go	21.62% <0.00%> (ø)
x/simulation/util.go	0.00% <0.00%> (ø)
x/nft/simulation/operations.go	68.36% <80.00%> (-3.07%)	⬇️
x/authz/simulation/operations.go	67.12% <100.00%> (ø)
x/bank/simulation/operations.go	81.84% <100.00%> (ø)
x/gov/simulation/operations.go	85.27% <100.00%> (ø)
x/group/simulation/operations.go	68.08% <100.00%> (ø)
x/slashing/simulation/operations.go	59.09% <100.00%> (ø)
... and 36 more