Add minLevel constructor parameter to all writers

[passsy]

Summary

• Adds minLevel constructor parameter to RotatingFileWriter, PrintConsoleWriter, and DeveloperLogConsoleWriter
• Provides a convenient way to set minimum log level directly in the constructor instead of chaining setMinLogLevel()

Example

// Before - requires chaining
final writer = RotatingFileWriter(
  baseFilePath: '/var/log/app.log',
)..setMinLogLevel(ChirpLogLevel.warning);

// After - constructor parameter
final writer = RotatingFileWriter(
  baseFilePath: '/var/log/app.log',
  minLevel: ChirpLogLevel.warning,
);

Test plan

• Added tests for minLevel constructor parameter on all three writers
• Verified filtering works correctly when used with ChirpLogger
• Verified minLogLevel property is set correctly
• All 819 existing tests pass

Closes #27

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