docs: enhance documentation with emojis

[allisson]

Update documentation files with emoji icons for better visual hierarchy and readability.

Add comprehensive read-write locks example demonstrating shared and exclusive lock patterns.

Changes:

• Add emojis throughout README.md, QUICKREF.md, and examples/README.md for improved visual navigation and user experience
• Create new examples/read-write-locks/main.go with three scenarios: concurrent readers, writer blocking readers, and readers blocking writer
• Update .golangci.yml to enable gocritic linter and configure goimports/golines formatters with project-specific settings
• Document read-write lock use cases including cache management, configuration access, and report generation coordination

The new example demonstrates how RLock/RUnlock allows multiple concurrent readers while Lock/Unlock provides exclusive access for writers.