feat: add log rotation support

[devfeel]

Summary

Add log rotation support for FileTarget and JSONTarget.

Changes

New Features

• Add rotator.go with SizeRotator and TimeRotator implementations
• Add rotation support to JSONTarget (was not implemented)
• Add MaxBackups config option to control backup file cleanup
• Add time-based rotation support (TimeRotator)

Bug Fixes

• Fix FileTarget concurrency issue with sync.Mutex
• Fix directory creation order (create dir before rotation check)

Configuration

Size-based Rotation (FileTarget)

targets:
  file:
    - name: FileLogger
      fileName: ./logs/app.log
      fileMaxSize: 10240  # KB
      maxBackups: 5        # keep 5 backup files

Size-based Rotation (JSONTarget)

targets:
  json:
    - name: JSONLogger
      fileName: ./logs/app.json
      fileMaxSize: 10240
      maxBackups: 5
      prettyPrint: true

Test Results

Item	Status
Build	✅ Pass
Test	✅ Pass

Files Changed

• targets/rotator.go (new)
• targets/target_file.go
• targets/target_json.go
• config/config.go
• config/json.go
• config/yaml.go

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