DEVSVCS-2328: remove duplicate request digests

[eutopian]

• move validation of mutable fields check to only create
  • This prevents "bricking" existing workflows if the limits are ever changed. Since the fields are immutable, updates cannot change the value of the existing workflows
• dedupe allowlist requests
  • Store the index of the digest in the mapping instead of the expiry time.
  • When populating the request digest list, create array with exact size the first time instead of shrinking

[github-actions]

Static analysis results are available

Hey @eutopian, you can view Slither reports in the job summary here or download them as artifact here.
Please check them before merging and make sure you have addressed all issues.