fix duplication of ports in AllocatedResources

[cgbaker]

#9367 suggests that the canonicalization of structs.Allocation.AllocatedResources is mutating the memdb object, causing the number of ports to grow on every call

there are a few solutions here:

• rewrite canonicalize to avoid this; this allows the field to exist and attempts consistency, which is presumably what we wanted to avoid
• mutate a copy

documenting test in the first commit:
https://app.circleci.com/pipelines/github/hashicorp/nomad/13195/workflows/63c91dd0-ea6e-440e-b080-50b68b680dbc/jobs/118749

copy-based fix in the second commit:
https://app.circleci.com/pipelines/github/hashicorp/nomad/13196/workflows/c857a136-5584-4d3f-ad10-6684bc7f9c68/jobs/118744

[nickethier]

Nice find

[github-actions]

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