test: Added tests for DecCoins to increase code coverage (#9752)

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## Description

Ref: #7031 

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Note/todo : 
1. Not sure if [this](https://github.com/cosmos/cosmos-sdk/blob/spoorthi/7031-deccoins-adding-tests/types/dec_coin.go#L631) line is reachable. The condition is already checked in [this ](https://github.com/cosmos/cosmos-sdk/blob/spoorthi/7031-deccoins-adding-tests/types/dec_coin.go#L618) line. Therefore, 100% coverage for `ParseDecCoin` function likely not possible
2. Clarification needed [here](https://github.com/cosmos/cosmos-sdk/blob/spoorthi/7031-deccoins-adding-tests/types/dec_coin_test.go#L883-L884)
3. Clarification needed [here](https://github.com/cosmos/cosmos-sdk/blob/spoorthi/7031-deccoins-adding-tests/types/dec_coin_test.go#L1124-L1125)

---

### Author Checklist

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I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [x] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) 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)

container/option_test.go

@@ -0,0 +1 @@
+package container_test