Add rust_decimal faking capabilities

[asaphaaning]

Thank you for providing this excellent tool!

This PR introduces Decimal faking.
I chose not to localize it and go with an enum for configuation. I will most likely supply more configuration options in the future :)

[cksac]

thanks for the PR, why use enum for config instead of use each variant as config object?

[asaphaaning]

thanks for the PR, why use enum for config instead of use each variant as config object?

For me to use the variants as config objects they would have to be structs, right?
I thought this was more concise but I am happy to change to what you prefer!

[cksac]

yes, please use struct for each variant. thx

[asaphaaning]

Already done!

[mothsART]

No tests in fake/tests/determinism.rs ?

[asaphaaning]

No tests in fake/tests/determinism.rs ?

Ah, will add tonight. 👍