docs(workflows): document step.sleep numeric duration as milliseconds

[HaoChiBao]

Summary

• Correct step.sleep numeric duration units from "seconds" to "milliseconds" in the Workers API and Python API references.

Fixes #32100.

Why

/workflows/build/sleeping-and-retrying/ already documents a bare number as milliseconds. The API reference pages said seconds. Callers who pass 30 expecting a 30s pause get a 30ms sleep and hot-loop. Duration strings ("30 seconds") are unchanged.

Verification

• Canonical docs already state ms: sleeping-and-retrying.mdx ("number (milliseconds)").
• Upstream tests treat bare numbers as ms: cloudflare/workers-sdk packages/workflows-shared/tests/binding.test.ts uses await step.sleep("sleep", 250) inside a flow that completes well under a multi-second test timeout — that cannot be 250 seconds.
• Same suite uses step.sleep("checkpoint", 1) as a near-instant checkpoint in engine.test.ts.

Test plan

• Workers API + Python API bullets agree with sleeping-and-retrying
• No remaining "in either seconds" wording for step.sleep duration on these pages
• Preview pages render the updated bullets

[cloudflare-docs-bot]

Review

✅ No issues found in commit 0c93575.

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