fix: handle AMF3 JSON values and invalid decode input

[skyswordw]

Summary

• encode AMF3 JSON values in CyberChef for booleans, null, arrays, strings, numbers, and plain objects instead of routing those cases through the broken @astronautlabs/amf Value.any() path
• keep AMF0 encoding on the existing library path
• convert empty, invalid, or truncated AMF decode input into clear CyberChef OperationError messages instead of surfacing low-level parser errors
• keep AMF encode and decode coverage in the existing AMF.mjs operation test file

Fixes #2490.
Fixes #2491.
Fixes #2492.

Validation

• npx grunt configTests
• focused AMF operation tests (11 passing)
• npm run lint
• NODE_OPTIONS=--openssl-legacy-provider npm test (245 Node API tests and 1971 operation tests passing)
• git diff --check

Notes: npm ci completed under Node v24.16.0 earlier in this branch. It reported the repository's existing deprecation/audit warnings, including 36 vulnerabilities; no dependency changes were made.

Development disclosure

I developed this change collaboratively with OpenAI Codex, with local review and validation before submission.

[skyswordw]

Thanks, I went with option 2 here. The AMF decode tests have been folded into AMF.mjs, AMFDecode.mjs has been removed from the operation test imports, and I added a small AMF3 encode/decode round-trip smoke test.

Validated locally with Node v24.16.0:

• focused AMF operation tests (11 passing)
• npm run lint
• NODE_OPTIONS=--openssl-legacy-provider npm test (245 Node API tests and 1971 operation tests passing)
• git diff --check

[GCHQDeveloper581]

Just checking - this PR is showing as "Draft"/"Not Ready" which indicates that it is not yet ready for merge. If you are still working on it that's absolutely fine, but if it's actually ready for formal review then could you change the state to "Ready for Review".

[skyswordw]

Thanks for checking. The follow-up change is in and the review thread is resolved, so I will move this to Ready for Review now.