Overhaul code coverage pipeline and Codecov configuration

[Kyle-Ye]

Summary

• Tighten project coverage threshold from 5% to 1%
• Enable 70% patch coverage target for PR-level feedback on new code
• Add platform flags (macos, ubuntu, ios) to distinguish coverage uploads
• Add PR comment configuration with header, diff, flags, files layout
• Add flag_management with carryforward support for per-flag statuses
• Upgrade Ubuntu codecov-action from v3 to v5 (align with macOS)
• Add Codecov upload step to iOS workflow using swift_project parameter

Test plan

• Verify macOS CI passes and uploads coverage with macos flag
• Verify Ubuntu CI passes and uploads coverage with ubuntu flag
• Verify iOS CI passes and uploads coverage with ios flag
• Verify Codecov PR comment appears with header, diff, flags, files layout
• Verify patch coverage status check appears on this PR
• If iOS swift_project auto-discovery fails, switch to explicit xcrun xccov fallback

[augmentcode]

🤖 Augment PR Summary

Summary: Updates Codecov configuration and CI workflows to give clearer PR-level coverage feedback across platforms.

• Enables patch coverage status with a 70% target and tightens the project status drop threshold to 1%.
• Adds flag_management with carryforward to support per-flag statuses for platform-specific uploads.
• Configures Codecov PR comments to include header, diff, flags, and files sections.
• Upgrades Ubuntu’s Codecov action to v5 and adds platform flags for macOS/Ubuntu/iOS uploads.
• Adds a Codecov upload step to the iOS workflow (including swift_project metadata).

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[augmentcode]

Review completed. 1 suggestions posted.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 29.01%. Comparing base (1a57428) to head (1a91f6a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #207 +/- ##
===========================================
+ Coverage 10.12% 29.01% +18.89% 
===========================================
Files 28 70 +42 Lines 820 2550 +1730 ===========================================
+ Hits 83 740 +657 - Misses 737 1810 +1073 

Flag	Coverage Δ
ios	29.03% <ø> (?)
macos	10.14% <ø> (?)
ubuntu	0.00% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.
see 43 files with indirect coverage changes

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