Refactor verification logic into dedicated module and modify verify_issue_bundle function

[dmidem]

This PR extracts and reorganizes the verification logic for asset burn and issuance into a new verification module (and submodules) and modifies the verify_issue_bundle function. These new verification modules could be potentially moved to the Zebra repository for further integration.

1. New Verification Module & Folder

   • Created a verification.rs module and a verification/ folder to house all verification-related logic.

2. Relocation of burn.rs

   • Moved the entire burn.rs file (containing the validate_bundle_burn function) to verification/burn.rs.

3. Refactoring verify_issue_bundle

   • The verify_issue_bundle function was moved from issuance.rs to verification/issuance.rs.
   • Its signature was updated to use a get_asset_state method (closure/trait) instead of relying on a finalization set.

4. Removed supply_info.rs Module

   • The SupplyInfo struct and related tests have been removed entirely, as the verification function (verify_issue_bundle) now returns a HashMap instead of SupplyInfo.
   • The AssetSupply struct definition, previously in supply_info.rs, has been moved to issuance.rs for consistency.

5. Test Updates & Extensions

   • All existing tests for the moved code were also relocated under the new verification folder.
   • Adjusted the tests to align with the revised verify_issue_bundle signature (using get_asset_state).

6. Retention of verify_supply in issuance.rs

   • The verify_supply method remains in issuance.rs, as it is still needed when the IssueBundle is signed in that module.

7. Visibility Fixes in issuance.rs

   • Since verify_issue_bundle tests have been moved to a separate module, certain fields in IssueBundle, IssueAction, and Signed structs were made pub(crate) so they can be accessed from verification/issuance.rs.
   • FIXME comments were added to indicate these visibility changes may need revisiting in the future.

TODO: Extend the test set in verification/issuance.rs to verify the correct handling of issued asset states in a global store context.

[dmidem]

Closed in favour #138