Add e2e test for context pruning threshold accuracy #6071

Job	Run time
build-and-check	3m 12s
test-integration-packages/internal	1m 5s
test-integration-packages/billing	1m 1s
test-integration-common	46s
test-integration-packages/agent-runtime	44s
test-integration-web	45s
test-integration-sdk	1m 23s
test-packages/billing	45s
test-integration-cli	39s
test-cli	54s
test-packages/agent-runtime	41s
test-.agents	46s
test-web	51s
test-common	43s
test-packages/internal	49s
test-sdk	46s
	15m 50s

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