refactor: replace zap with slog

[danielandersson]

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This PR replaces the third-party Zap logging library with Go's standard library slog package for structured logging. This change reduced the number of dependencies while maintaining the same logging functionality and format.

Fixes #2120

Changes

• Removed dependencies on go.uber.org/zap and go.uber.org/zap/zapcore
• Added usage of Go's standard library log/slog package
• Simplified the StdLogger structure by combining infoLog and debugLog into a single stdLog
• Refactored the StructuredLogger to use slog.Logger instead of Zap's SugaredLogger
• Modified the NewStructuredLogger function to use slog handlers and configuration
• Added a new replaceAttr function to maintain compatibility with Google Cloud Logging format
• Ensured that log messages continue to adhere to the LogEntry format for Google Cloud Logging