feat: get metadata b64 by key

[cusma]

No description provided.

[Copilot]

Pull request overview

This PR adds a new ABI method arc89_get_metadata_b64_bytes_by_key that retrieves and decodes base64-encoded values from ASA metadata. The feature supports both URL-safe and standard base64 encoding schemes.

Key Changes

• Added arc89_get_metadata_b64_bytes_by_key method that fetches a base64-encoded string from JSON metadata and returns the decoded bytes
• Renamed AsaMetadataRegistryInterface to Arc89Interface for clarity
• Enhanced documentation for existing metadata getter methods with improved formatting and clarity

Reviewed changes

Copilot reviewed 7 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/test_arc89_get_metadata_b64_bytes_by_key.py	New test file with tests for both URL-safe and standard base64 encoding
tests/conftest.py	Added test data for base64-encoded values (both URL-safe and standard encodings)
smart_contracts/asa_metadata_registry/errors.py	Added validation error message for invalid base64 encoding parameter
smart_contracts/asa_metadata_registry/enums.py	Added enum constants for base64 encoding types (URL-safe = 0, Standard = 1)
smart_contracts/asa_metadata_registry/contract.py	Implemented new method with validation, decoding logic, and improved documentation for existing methods
smart_contracts/asa_metadata_registry/arc89_interface.py	Renamed interface class and added abstract method signature for the new feature
smart_contracts/artifacts/asa_metadata_registry/AsaMetadataRegistry.approval.teal	Updated compiled TEAL code with new method implementation

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