Use simplicityhl-std in lending-contracts

[Hrom131]

Describe the feature

Describe the feature

Description

To improve the code quality of Simplicity contracts within the lending-contracts crate, it is necessary to use the simplicityhl-std crate.

To support modules within Simplicity contracts, Simplex must also be updated to version 0.0.7.

Acceptance Criteria:

• Simplex 0.0.7 version
• Safe math operation from the simplicityhl-std
• Helper functions from the simplicityhl-std
• Separate .simf files with duplicated utility functions