Align AEAD key-nonce docs with runtime contract

[Keemosty12]

Describe your changes

This PR aligns AEAD key/nonce ordering across MASM comments, handler documentation, and user-facing docs to match the actual runtime/event contract (key then nonce).
It removes contradictory contract descriptions that could cause integration or review mistakes, while keeping behavior and APIs unchanged.

Checklist before requesting a review

• Repo forked and branch created from next according to naming convention.
• Commit messages and codestyle follow conventions.
• Commits are signed.
• Relevant issues are linked in the PR description.
• Tests added for new functionality.
• Documentation/comments updated according to changes.
• Updated CHANGELOG.md

[github-actions]

Automated check (CONTRIBUTING.md)

Findings:

• Link an issue in the PR body (e.g., "Fixes Implement SHA256 in Miden Assembly #123").
• Add a short Rationale explaining why the change is needed.

Recommendations:

• Consider adding a Test plan or clear review steps.

Next steps:

• Link a relevant issue (e.g., "Fixes Implement SHA256 in Miden Assembly #123") and ensure it is assigned to you.
• See CONTRIBUTING.md for expectations.
• If this is a false positive, comment: /quality-review.

[huitseeker]

This partially addresses the broader core-lib docs drift tracked in #2694. In particular, #2547 moved the executable contract toward the unified LE stack convention, but some user-facing and inline AEAD docs kept the older key/nonce wording.

[Al-Kindi-0]

LGTM, thanks for fixing these