[KIP-932] Add tests for user callbacks in share consumer 2/N

[Kaushik Raina (k-raina)]

Summary

• Add 21 tests for ShareConsumer callbacks (error_cb, log_cb, oauth_cb, stats_cb, throttle_cb) across the unit and integration suites
• Unit: error_cb dispatch + exception propagation through poll/commit_sync/commit_async/close; oauth_cb principal+extensions, token-refresh success & failure-recovery, malformed-return; log_cb drain on
  commit/close, record format, and always-on (non-debug) delivery; stats_cb / statistics.interval.ms=0 rejection edges.
• Integration: assert share-specific log facility tags (SHAREFETCH/SHAREACK/SHARESESSION/SHAREHEARTBEAT) and the cleared throttle_time=0 throttle event.
• Add a provision_client_quota fixture so throttle tests self-provision/tear-down quotas and run unattended in CI — replacing the manual SHARE_THROTTLE_QUOTA_CLIENT_ID env-var gating.
• Document a real crash via 3 skipped tests: calling a ShareConsumer method from inside a generic callback SIGSEGVs (librdkafka's reentrancy guard covers only the ack-commit cb); cross-thread correctly raises _CONFLICT — un-skip and assert _STATE once the guard is extended.

[confluent-cla-assistant]

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[sonarqube-confluent]

Quality Gate failed

Failed conditions
1.2% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube