Emit all logs as JSON for logs-ingester compatibility

[matteogastaldello]

This pull request updates the logging approach in main.go to use the structured logger (slog) instead of the standard library's log package, and improves error reporting for the pprof and main HTTP servers.

Logging improvements:

• Replaced the import of the standard log package with log/slog and removed all usage of log.Println, switching to the structured logger for consistency and better log formatting.
• Updated the pprof server goroutine to log errors using log.Error with structured fields, instead of printing them directly.
• Improved error logging for the main HTTP server by using structured logging with address and error fields, instead of formatting them into a string.Route pprof server errors and the server listen error through the slog JSON logger instead of stdlib log/printf-style calls, so every emitted line is a valid JSON object.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
main.go	0.00%	4 Missing ⚠️

📢 Thoughts on this report? Let us know!