better memory management

[PaulLaux]

Improved memory management and compatibility by replacing &vec<u8> to &[u8] in some places and some other minor changes.

[what-the-diff]

PR Summary:

• Function Signature Modifications to Improve Performance and Memory Usage
  This PR includes changes in our function signatures to use slices instead of vectors for asset descriptions throughout various files. This alteration will enhance our application's performance and reduce memory usage.

• Optimization of get_all_notes Return Value in issuance.rs
  The get_all_notes function has been modified to return a vector of references instead of owned vectors. This change will avoid unnecessary cloning and improve application performance.

• Function Renaming for Improved Clarity
  The function formerly known as get_actions_by_base has been renamed to get_actions_by_asset in the file issuance.rs for improved clarity and understandability.

• Standardization of Formatting and Syntax
  To uphold consistency and clarity in the codebase, minor formatting and syntax changes have been made that do not impact the overall functionality.