Update flow-nft contracts to comply with Stable Cadence changes

[sisyphusSmiling]

Problem

Changes to Cadence are coming and we'll want to make sure that the contracts function beyond the upcoming breaking changes.

See this epic for additional context.

Acceptance Criteria

Assignee should refer to the merged and upcoming changes in this forum post and cover all occurrences of incompatible syntax in existing repo contracts. All contracts should be compatible with the soon to be updated version of Cadence.

[sisyphusSmiling]

In progress on #126