* test: replace 61 live logging and otel tests with offline unit and integration coverage
* test: restore datadog formatting, deliver datadog logs and redis failures over the wire, assert full router hook payloads, tighten stream usage and otel checks
Restores the pre-existing test_datadog.py lines the branch had reflowed. Datadog success, failure and redis-failure replacements now assert the gzip body posted to the intake, with redis failing through a real cache on a closed local port. Router hook sequence recorder checks the legacy field types and asserts concrete payloads, exact streaming and fallback sequences. Stream usage asserts the default include_usage request body and the redacted messages value. Otel asserts response id and token counts.
* test: assert budget envelope figures, guardrail inspection and exact prometheus samples per request
* test: isolate the prometheus latency test on its own deployment so counts do not depend on order
* test: cover timed slack delivery, keep the redis failure test off the network, and make new payload types read-only
* test: drain the redis test's logging and scope otel span checks to the test's own trace
* test: drive the periodic slack flush without a wall-clock interval
* test: scope router hook events to the test, script the db clock, split a nested comprehension
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Co-authored-by: yuneng <yuneng@berri.ai>
