[2026 Assets] Validate asset issuers and trustline authorization state

[Nanle-code]

Objective

Distinguish valid issuers, missing issuers, authorization-required assets, and clawback-enabled assets.

Target area

asset and trustline components

Acceptance criteria

• The objective is implemented with clear handling for invalid input, unsupported environments, and failure paths.
• Automated tests cover the primary flow, at least one boundary case, and at least one failure case.
• User-facing documentation or developer guidance is updated, including compatibility, security, or migration notes where applicable.

Source: .github/roadmap-issues-2026-07-29.json.