Add fee calculation implementation & test coverage

[sisyphusSmiling]

Issue To Be Solved

The bridge will need to charge fees for the sake of funding account storage and to prevent spam. Fees are currently broken down to cover the following:

• onboarding assets: deploying contracts and initializing escrow to lock assets
• base fee: a flat rate fee included for every bridge request
• storage rate: the cost basis for each stored byte

Suggest A Solution

The fee to bridge an asset should be at least as much as it costs the bridge account to escrow the asset, if it needs to be escrowed at all.

This issue relates to the functionality of setting fees and validating bridging behavior when those fees are set, not necessarily the economics of the fee amount in question. In addition to fee feature integration, we will also need to consider and test the impact of the fee rates we choose to set at scale and ensure the final amounts safeguards against potential storage ddos vectors.