perf: optimize sleep session db storage calls

[apedley]

[!TIP]

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Description

What problem does this PR solve?
Syncing large amounts of data will timeout due to a lot of db calls.

How did you implement the solution?
Sync smaller batches for sleep sessions and optimize db calls for sleep sync functions.

Linked Issue: Closes #1263

How to Test

1. Sync a large amount of data

PR Type

• Issue (bug fix)
• New Feature
• Refactor
• Documentation

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Screenshots

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PR Validation Results

Change Detection

• ⚙️ Backend changes detected
• 📱 Mobile changes detected

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[gemini-code-assist]

Code Review

This pull request optimizes the synchronization of health data by separating sleep sessions from other session types. On the mobile client, sleep sessions are now chunked into smaller batches (SESSION_CHUNK_SIZE = 50) to prevent timeouts, while exercise and workout sessions remain grouped by source to support the server's range-delete behavior. On the server side, sleep session processing is optimized by pre-fetching and sharing the user profile and timezone context across the batch, eliminating redundant database queries. The reviewer suggested memoizing the context promise instead of the resolved value in getSleepContext to prevent potential race conditions and duplicate queries if the batch processing is refactored to run concurrently in the future.

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