fix: properly convert internal Metadata to v3 api Labels type

[gergely-kurucz-konghq]

Summary by CodeRabbit

• Refactor
  • Improved internal metadata handling consistency across billing, customer, meter, subscription, and app services through standardized conversion logic.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR unifies metadata-to-labels conversion across API handlers by changing ConvertMetadataToLabels to accept models.Metadata instead of map[string]string. It removes duplicate conversion helpers from generated code and implements the standardized function across multiple handler packages (apps, billing profiles, customers, meters, subscriptions), while updating the App interface and its implementation to use strongly-typed metadata.

Changes

Cohort / File(s)	Change Summary
Apps handler metadata conversion api/v3/handlers/apps/convert.go, api/v3/handlers/apps/convert.gen.go	Updated ConvertMetadataToLabels signature from map[string]string to models.Metadata, removed generated helper, and implemented new function to populate labels from source metadata.
Billing profiles handler api/v3/handlers/billingprofiles/convert.gen.go, api/v3/handlers/billingprofiles/convert.go	Removed duplicate billingMetadataToPV3Labels and billingMetadataToV3Labels helpers, added new ConvertMetadataToLabels accepting billing.Metadata.
Customers handler api/v3/handlers/customers/convert.gen.go, api/v3/handlers/customers/convert.go	Removed modelsMetadataToV3Labels and pModelsMetadataToPV3Labels helpers, added new ConvertMetadataToLabels accepting pointer to models.Metadata.
Meters handler api/v3/handlers/meters/convert.gen.go, api/v3/handlers/meters/convert.go	Removed modelsMetadataToPV3Labels and modelsMetadataToV3Labels helpers, added new ConvertMetadataToLabels accepting models.Metadata.
Subscriptions handler api/v3/handlers/subscriptions/convert.go	Replaced direct api.Labels construction with new unexported convertMetadataToLabels helper ensuring non-nil labels.
App type changes openmeter/app/app.go, openmeter/app/appbase.go	Changed GetMetadata() return type and Metadata field from map[string]string to models.Metadata.
App HTTP driver openmeter/app/httpdriver/mapper.go	Updated Stripe and Custom Invoicing metadata handling to use api.Metadata() wrapper on result of GetMetadata().

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• openmeterio/openmeter#3782: Directly modifies the same ConvertMetadataToLabels function signature in apps conversion layer that this PR refactors.
• openmeterio/openmeter#2678: Changes metadata type from map[string]string to models.Metadata and updates ConvertMetadataToLabels usages across handlers.
• openmeterio/openmeter#3794: Modifies metadata handling in customer billing and App metadata surfaces with similar type conversions.

Suggested labels

area/api, area/apps

Suggested reviewers

• tothandras

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: consolidating metadata-to-labels conversion logic across multiple handlers by introducing new ConvertMetadataToLabels functions and updating the App interface to use a strongly-typed models.Metadata type.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/api-v3-handlers-labels-empty

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