test: Added tests for DecCoins to increase code coverage

[spoo-bar]

Description

Ref: #7031

Note/todo :

1. Not sure if this line is reachable. The condition is already checked in this line. Therefore, 100% coverage for ParseDecCoin function likely not possible
2. Clarification needed here
3. Clarification needed here

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #9752 (d991bc3) into master (adff7d8) will increase coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head d991bc3 differs from pull request most recent head 3a3b80a. Consider uploading reports for the commit 3a3b80a to get more accurate results

@@            Coverage Diff             @@
##           master    #9752      +/-   ##
==========================================
+ Coverage   63.46%   63.47%   +0.01%     
==========================================
  Files         563      563              
  Lines       37504    52726   +15222     
==========================================
+ Hits        23801    33468    +9667     
- Misses      11839    17358    +5519     
- Partials     1864     1900      +36     

Impacted Files	Coverage Δ
client/flags/flags.go	21.05% <0.00%> (-1.17%)	⬇️
x/staking/migrations/v040/migrate.go	50.94% <0.00%> (-10.60%)	⬇️
x/genutil/genesis.go	40.00% <0.00%> (-10.00%)	⬇️
x/evidence/keeper/infraction.go	78.40% <0.00%> (-9.83%)	⬇️
client/keys/import.go	57.14% <0.00%> (-7.57%)	⬇️
store/cache/cache.go	79.62% <0.00%> (-7.47%)	⬇️
x/distribution/keeper/hooks.go	23.68% <0.00%> (-7.27%)	⬇️
x/slashing/keeper/unjail.go	41.17% <0.00%> (-6.83%)	⬇️
crypto/keyring/output.go	36.11% <0.00%> (-6.75%)	⬇️
types/codec.go	60.00% <0.00%> (-6.67%)	⬇️
... and 554 more

[orijbot]

Visit https://dashboard.github.orijtech.com?pr=9752&repo=cosmos%2Fcosmos-sdk to see benchmark details.

[cyberbono3]

lgtm

[alessio]

Welcome aboard @spoo-bar! Grab a drink and fasten your belt: it's going to be a fun ride.