fix: package comments, error return and deadlock fix

[rustatian]

Description of Changes

• Fix deadlock in the status logic.
• Correctly return error from the pool's channel.
• Add package comments.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The reason for this PR is clearly provided (issue no. or explanation).
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.

Summary by CodeRabbit

• New Features

  • Improved PHP worker error propagation for better diagnostics.

• Bug Fixes

  • Fixed potential null pointer issue in error handling.
  • Enhanced file error detection during parsing operations.
  • Improved mutex synchronization reliability.

• Documentation

  • Added package-level documentation comments for better code clarity.

• Chores

  • Updated CI environment to PHP 8.5.
  • Updated artifact download action to latest version.
  • Minor code formatting improvements.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds package-level documentation comments across multiple files, improves error handling in file operations and worker communication, refactors mutex management using defer patterns, and updates GitHub Actions workflows with PHP version 8.5 and artifact download action v5.

Changes

Cohort / File(s)	Summary
Documentation Comments api/interfaces.go, codec/codec.go, plugin.go, protoc_plugins/protoc-gen-php-grpc/main.go, protoc_plugins/protoc-gen-php-grpc/php/generate.go	Package and file-level documentation comments added to describe gRPC plugin components, codec behavior, and code generation functionality.
Error Handling Improvements parser/parse.go, proxy/proxy.go	File open errors now properly checked and returned; worker error propagation changed to surface actual worker errors instead of local errors.
Mutex & Status Handling health_server.go, server.go	SetServingStatus uses defer for mutex unlock; interceptor error/status handling refactored to use condition-based switch with nil-safe error handling and explicit default case.
CI Workflow & Formatting .github/workflows/linux.yml, protoc_plugins/protoc-gen-php-grpc/php/template.go	PHP version bumped to 8.5; artifact download action updated to v5; consolidation of test script into single inline string; whitespace cleanup in template function map.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A hop, skip, and bounds of care,
Package docs float through the air,
Errors caught with proper grace,
Defers unlock their mutex embrace,
Clean and clear, this code's now fair! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title accurately summarizes the three main changes: package comments, error return fix, and deadlock fix. It is concise, specific, and clearly communicates the primary objectives.
Description check	✅ Passed	The PR description includes the required sections with specific change details, license acceptance, and a completed checklist. However, it lacks a 'Reason for This PR' section with an issue reference.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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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/return-correct-error

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[Copilot]

Pull request overview

This PR addresses three critical bug fixes and adds missing package documentation:

Changes:

• Fixed a deadlock in the health check server by properly positioning the mutex unlock using defer
• Corrected error return in the proxy to return the payload error instead of the wrong error variable
• Added package-level comments to all packages following Go documentation conventions

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
health_server.go	Fixed deadlock by moving defer h.mu.Unlock() to immediately after lock acquisition in SetServingStatus
proxy/proxy.go	Fixed bug where wrong error variable was returned; now correctly returns pl.Error()
server.go	Enhanced status code determination logic to handle nil error case with explicit default
parser/parse.go	Added proper error handling for file open operation
plugin.go	Added package comment describing the gRPC server plugin
api/interfaces.go	Added package comment for API interfaces
codec/codec.go	Added package comment for codec implementation
protoc_plugins/protoc-gen-php-grpc/main.go	Added command documentation comment
protoc_plugins/protoc-gen-php-grpc/php/generate.go	Added package comment for PHP code generation
protoc_plugins/protoc-gen-php-grpc/php/template.go	Removed extraneous blank lines for cleaner formatting
go.work.sum	Automatic dependency checksum updates

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (a930720) to head (780ec78).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@      Coverage Diff      @@
##   master   #142   +/-   ##
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