docs(power): clarify replay safety and step semantics

[embano1]

Update the durable-functions power guidance to distinguish deterministic orchestration code from non-atomic durable operation bodies.

• generalize replay-safety guidance across steps, waits, and concurrent branches
• document logger replay caveats and note that context.logger can wrap an existing logger
• correct StepSemantics defaults and examples for TypeScript and Python
• document the at-most-once-per-retry fallback for non-idempotent steps with retries disabled

Issue #, if available:

Description of changes:

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[embano1]

FYI, I also have another branch ready (based on these changes), which reduces the power size by ~50%.

[embano1]

@singledigit can you use this updated power to verify if it would have caught the bugs in your scanner function: https://github.com/singledigit/durable-function-video-scanner/tree/main

Scanner fix: generate stable Transcribe/Rekognition submission identifiers once from durable state, not from wall-clock time inside the callback submitter. Default: derive them from scanId plus a deterministic suffix, or generate them in an earlier durable step and reuse them in the submitter.
Scanner fix: replace handler-level logger.* calls with context.logger (and childContext.logger / submitter ctx.logger where available) for all logging that can occur during replay.