feat: make log output non-blocking

[rustatian]

Reason for This PR

Keep log calls responsive when the output reader is slow.

closes: roadrunner-server/roadrunner#2195

Description of Changes

• Make asynchronous output the default for all logger formats and channels.
• Queue up to 1,024 copied records in a buffered channel and discard new messages when it is full.
• Start all output drains before waiting for shutdown. Report output errors.

License Acceptance

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

PR Checklist

• All commits in this PR are signed (git commit -s -S).
• The reason for this PR is clearly provided.
• The description of changes is clear and complete.
• Required documentation changes are included.
• User-facing changes are documented in README.md.
• All added or changed functionality is tested.

[codecov]

Codecov Report

❌ Patch coverage is 96.77419% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.45%. Comparing base (d6f3c21) to head (9e54468).

Files with missing lines	Patch %	Lines
async_writer.go	95.91%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #117      +/-   ##
==========================================
+ Coverage   83.88%   87.45%   +3.57%     
==========================================
  Files           5        6       +1     
  Lines         242      295      +53     
==========================================
+ Hits          203      258      +55     
+ Misses         39       37       -2     

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[Copilot]

Copilot review overview

🟡 Changes recommended

Serial shutdown can starve healthy logger queues behind one blocked output.

Review effort: Balanced
Findings: 1

Open (1)

• Initiate all writer shutdowns concurrently before waiting · New

What changed in this PR

Adds bounded asynchronous logging to prevent slow output readers from blocking application work.

Changes:

• Adds a 1 MiB asynchronous output queue with drop/error reporting.
• Adds deadline-aware shutdown draining.
• Documents and tests asynchronous behavior.

File	Description
README.md	Documents buffering and shutdown behavior.
plugin.go	Adds deadline-aware output shutdown.
logger.go	Drains channel outputs on close.
config.go	Wraps enabled outputs asynchronously.
async_writer.go	Implements asynchronous queued writing.
async_writer_test.go	Tests queuing, blocking, and shutdown.
format_handler_test.go	Cleans up asynchronous output resources.

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