Harden MCP OAuth cancel E2E tests against create/interest race #1796

Job	Run time
Rust SDK Tests (ubuntu-latest, inprocess)	10m 42s
Rust SDK Bundled CLI Build (macos-latest)	3m 5s
Rust SDK Tests (macos-latest, inprocess)	11m 7s
Rust SDK Bundled CLI Build (ubuntu-latest)	2m 54s
Rust SDK Tests (ubuntu-latest, default)	9m 50s
Rust SDK Tests (windows-latest, default)	12m 18s
Rust SDK Bundled CLI Build (windows-latest)	4m 17s
Rust SDK Tests (macos-latest, default)	8m 41s
	1h 2m 54s

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