LP: Unitary testing for add_currency

[lemunozm]

Description

Changes and Descriptions

• Remove related tests from IT in cases/liquidity_pools.rs
• Add associated UTs
• Simplify wrapped token struct as tuple.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 30.76923% with 9 lines in your changes missing coverage. Please review.

Project coverage is 46.33%. Comparing base (551fb4c) to head (07ff058).

Files	Patch %	Lines
pallets/liquidity-pools/src/lib.rs	36.36%	7 Missing :warning:
libs/types/src/domain_address.rs	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1912 +/- ## ========================================== + Coverage 46.30% 46.33% +0.03% ========================================== Files 179 179 Lines 13081 13074 -7 ========================================== + Hits 6057 6058 +1 + Misses 7024 7016 -8 ```

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[lemunozm]

This is ready to be merged if you agree in the above clean up

[lemunozm]

Yeah, lp tests are not modified