DAOS-17089 cart: simplify progress callback registration

[soumagne]

Only support a single callback per context for now

Fix utest_swim not creating cart context

Required-githooks: true

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[github-actions]

Ticket title is 'simplify cart progress callback registration'
Status is 'Open'
https://daosio.atlassian.net/browse/DAOS-17089

[daltonbohning]

ftest LGTM (c-code actually)

[daltonbohning]

Is Intel copyright intentionally updated?

[soumagne]

Well I had worked on it while we were at Intel so I guess it would count :D

[frostedcmos]

LGTM, seems we indeed dont use multiple cbs anymore, so no need to keep complexity of keeping the array of them