Fix PSR-3 v3 compatibility for Logger class

[sangemaru]

Summary

Fixes fatal error when running SatisPress with PHP 8.x and psr/log ^3.0.

The log() method signature in SatisPress\Logger must match Psr\Log\AbstractLogger::log() which in psr/log 3.x requires:

• \Stringable|string type hint for $message parameter
• void return type

The Error

Fatal error: Declaration of SatisPress\Logger::log($level, $message, array $context = [])
must be compatible with Psr\Log\AbstractLogger::log($level, Stringable|string $message,
array $context = []): void in /path/to/satispress/src/Logger.php on line 73

Changes

• Updated log() method signature to match PSR-3 v3 interface
• Cast $message to string before passing to format() method (handles Stringable objects)
• Updated docblock to reflect new parameter types

Backwards Compatibility

This change maintains backwards compatibility:

• Still works with psr/log ^1.0 and ^2.0 (union types are valid, just not enforced)
• The (string) cast handles both string and Stringable inputs correctly

Test Plan

• Verified fix resolves fatal error on PHP 8.2 with psr/log 3.0
• Logging functionality works as expected with string messages
• Logging functionality works with Stringable objects