refactor: detailed line provisioning logic

[turip]

Overview

This patch duplicates the line provisioning logic for invoice lines and detailed lines in anticipation for #3514 this will make the PR more readable.

The code is almos an exact copy of the line provisioning logic as DetailedLine is a type alias for Line.

Summary by CodeRabbit

• Bug Fixes

  • Improved reliability when upserting detailed invoice lines, ensuring correct parent-child relationships and consistent handling of attributes (period, tax settings, subscription data, metadata).
  • Stricter validation: only usage-based invoice-level lines are accepted for upsert; invalid types now return clearer, contextual errors.

• Refactor

  • Simplified and consolidated the invoice line upsert flow for better maintainability and fewer edge cases.
  • Removed unused logic and reduced dependencies to streamline processing.

[coderabbitai]

📝 Walkthrough

Walkthrough

Removes DetailedLine diff generation with parent IDs and the samber/lo import. Refactors invoice line upsert flow: introduces invoiceLineUpsertConfig and a dedicated upsertDetailedLines path, enforces UsageBased type for invoice-level lines, and centralizes parent-child linkage and detailed line attribute handling with improved error wrapping.

Changes

Cohort / File(s)	Summary
Remove DetailedLine diff with parent IDs and lo dependency openmeter/billing/adapter/invoicelinediff.go	Deleted GetDetailedLineDiffWithParentID() and the samber/lo import; removes mapping-based construction of DetailedLine diffs including ParentLineID updates.
Refactor upsert flow for invoice and detailed lines openmeter/billing/adapter/invoicelines.go	Introduced invoiceLineUpsertConfig and upsertDetailedLines; split basic vs. detailed line handling; enforce UsageBased type for invoice-level lines; centralize parent-child linkage and detailed attributes; replace previous diff-based detailed-line upsert; improved contextual error handling.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~55 minutes

Possibly related PRs

• refactor: simplify invoicing api #2912 — Refactors invoice line models and parent/child handling, aligning with removal of GetDetailedLineDiffWithParentID and new detailed-line upsert flow.
• refactor: disambiguate line children #3237 — Modifies parent-child linkage in invoicelinediff.go and invoicelines.go, overlapping with this PR’s restructuring of detailed-line construction and iteration.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title succinctly indicates a refactor of detailed line provisioning logic, which aligns with a significant aspect of the changeset by highlighting the new dedicated detailed line upsert flow and the removal of the old mapping logic.

✨ 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 refactor/split-line-provisioning-logic

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