Ensure logging is configured on remote task workers

[devin-ai-integration]

When tasks run on remote Dask or Ray workers via a serialized context, the worker process may never have called setup_logging(). This means the APILogHandler is not attached to Prefect loggers and task run logs are silently lost.

Closes #18082

Changes

New API in prefect.logging.configuration:

• ensure_logging_setup() — idempotent function that calls setup_logging() only if PROCESS_LOGGING_CONFIG has not been populated. This keeps the internal state check encapsulated rather than leaking it to callers.
• is_logging_configured() — simple query for whether logging has been set up in this process.

Task engine (SyncTaskRunEngine / AsyncTaskRunEngine):

• In initialize_run(), after entering hydrated_context, call ensure_logging_setup() when self.context is not None (i.e., remote execution only — local task runs are unaffected).
• In the finally block, flush APILogHandler (sync) / await APILogHandler.aflush() (async) to ensure queued logs are sent before the task result is returned to the orchestrator.

Important review notes

• The flush approaches differ between sync and async: sync iterates handlers on the "prefect.task_runs" logger and flushes matching APILogHandler instances, while async calls APILogHandler.aflush() (a classmethod that calls APILogWorker.drain_all()). The async path flushes all enqueued logs globally, not just for the current task run — worth verifying this is acceptable.
• is_logging_configured() is added and tested but not called by the implementation itself (ensure_logging_setup() checks PROCESS_LOGGING_CONFIG directly). It's exposed as public API for external consumers.
• No integration-level test exercises the full path (task engine with serialized context → logging setup → flush). The unit tests cover the new configuration functions in isolation using the existing dictConfigMock fixture pattern.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

Link to Devin session: https://app.devin.ai/sessions/c7590302b0bc40df9fba83c32ba15f91
Requested by: @desertaxle

[devin-ai-integration]

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[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing devin/OSS-6581-1774992663 (f7bb258) with main (69775fb)}