Handle prefix in exp treatements by new endpoint (#333282)

* Handle prefix in exp treatements by new endpoint

* Update comment formatting

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Updates to make new endpoint win on collision

* Move scoped-treatment tests into a dedicated suite

Addresses PR review: the scoped-lookup tests do not exercise delegate
recreation, so they belong in their own suite rather than in
'ExP Service delegate recreation'.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 15b73982-0eed-4302-a104-a946d0382b4c

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 15b73982-0eed-4302-a104-a946d0382b4c