Bound OpenFeature provider initialization time

[leoromanovsky]

Motivation

The first agentless poll and its retries run on the provider activation thread before the provider timeout starts. With defaults, three 5-second requests and 12–18 seconds of retry delay can consume 27–33 seconds. The separate 30-second provider wait makes total failure time a calculated 57–63 seconds.

A controlled 500 ms blocked first poll with a 100 ms provider timeout took 617 ms before this change.

Changes and Decisions

• Start one initialization deadline before Feature Flags activation.
• Count synchronous activation time against the remaining provider wait.
• Schedule the first poll immediately on the existing configuration executor.
• Keep retry and late-recovery behavior on the configuration executor.
• Do not create an additional worker thread.

Validation

The same controlled blocked-poll test completed in 114 ms after the change. The 500 ms poll continued on the configuration thread and did not extend provider initialization.

[datadog-prod-us1-4]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 79.26% (+20.91%)

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