29-fee/types tests should use standard testing pkg: types_test

[damiannolan]

Summary

Tests maintained in 29-fee/types should be updated to follow the same testing package standard used throughout the ibc-go repository.

When writing tests I stumbled upon an import cycle when using ibctesting.MockFeePort, this can avoided by using:

package types_test

in favour of:

package types

All tests under pkg types will need to be updated to accommodate this

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