Fix duplicate iOS sleep-stage queries

[dmarttila]

Summary

• query HealthKit's sleep-analysis sample type once per date range instead of once per Dart alias
• map each native sleep category to one canonical requested HealthDataType while retaining legacy asleep-unspecified records
• preserve HealthKit sample UUID and native device identifier for reliable de-duplication and provenance
• consistently expose Apple-specific sleep-stage values as durations in minutes

Why

On iOS, SLEEP_DEEP and SLEEP_ASLEEP_DEEP both filter the same HealthKit category value, as do SLEEP_REM and SLEEP_ASLEEP_REM. SLEEP_ASLEEP also overlaps SLEEP_ASLEEP_CORE for Core records. Asking for the full iOS sleep set therefore returned the same native samples under multiple Dart types.

In a diagnostic export containing 951 sleep rows, all 80 Deep records, all 110 REM records, and 243 Core records were duplicated. There were only 518 unique time intervals, all from the same Apple Watch source.

The Apple-specific aliases also retained raw category values 3, 4, and 5 while declaring MINUTE as their unit. This change converts them from timestamps just like the generic sleep types.

Compatibility

• iOS callers can continue requesting the existing generic and Apple-specific type list.
• If both aliases are requested, Apple-specific Core/Deep/REM types are preferred and returned once.
• If only a generic alias is requested, the plugin returns that generic type.
• SLEEP_ASLEEP continues to include asleep-unspecified, and represents Core when SLEEP_ASLEEP_CORE was not requested.
• Android query behavior is unchanged.
• Samples without UUIDs retain the existing structural de-duplication behavior.

Verification

• flutter test test/health_test.dart: 4 tests passed
• xcrun swiftc -parse packages/health/ios/Classes/SwiftHealthPlugin.swift
• flutter build ios --simulator --no-codesign: succeeded
• git diff --check

The package-wide analyzer still reports its existing example-app info-level lint backlog; no new diagnostic points to the changed files.