test: improve test coverage for type tests in perp v2

[matthiasmatt]

Description

What does this PR do?

Purpose

Why is this PR important?

[codecov]

Codecov Report

Merging #1518 (2d27663) into master (4566d9f) will increase coverage by 3.22%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1518      +/-   ##
==========================================
+ Coverage   62.00%   65.23%   +3.22%     
==========================================
  Files         159      159              
  Lines       13914    13969      +55     
==========================================
+ Hits         8628     9112     +484     
+ Misses       4642     4211     -431     
- Partials      644      646       +2     

Impacted Files	Coverage Δ
x/common/testutil/cli/network.go	59.78% <100.00%> (ø)
x/inflation/types/params.go	73.91% <100.00%> (ø)
x/perp/v2/types/amm.go	87.55% <100.00%> (+20.59%)	⬆️
x/perp/v2/types/market.go	100.00% <100.00%> (+100.00%)	⬆️
x/perp/v2/types/msgs.go	92.10% <100.00%> (+92.10%)	⬆️
x/perp/v2/types/position.go	100.00% <100.00%> (+100.00%)	⬆️
x/spot/keeper/liquidity.go	59.37% <100.00%> (ø)
x/stablecoin/keeper/needed.go	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes