feat: limit open-ended vectors for covenants

[hansieodendaal]

Description

Limited open-ended vectors to guard against malicious network messages in:

• covenants

Motivation and Context

This is a defense-in-depth exercise.

How Has This Been Tested?

Existing unit tests pass.

What process can a PR reviewer use to test or verify this change?

Code review

Breaking Changes

• [x] None
• [ ] Requires data directory on base node to be deleted
• [ ] Requires hard fork
• [ ] Other - Please specify