Implement log/slog framework for structured logging

[Copilot]

This PR replaces the standard log package and fmt.Printf error logging with Go's modern log/slog framework to provide structured logging throughout the codebase.

Changes Made

Core Library

• api.go: Updated the AutoSave function to use slog.Error() instead of fmt.Printf() for error logging
• Added log/slog import to enable structured logging in the core API

Command-Line Tools

Updated all command-line tools in cmd/ to use structured logging:

• cmd/debug_matching/main.go
• cmd/target_performance/main.go
• cmd/performance_benchmark/main.go

Example Applications

Updated all example applications in example/ to use structured logging:

• example/main.go
• example/clustered/main.go
• example/forest_demo/main.go
• example/brokers_demo/main.go
• example/dimension_consistency/main.go
• example/multitenant_demo/main.go
• example/weight_conflict_demo/main.go

Logging Format Changes

Before:

log.Printf("Failed to add rule: %v", err)
fmt.Printf("Auto-save error: %v\n", err)
log.Fatalf("Failed to create matcher: %v", err)

After:

slog.Error("Failed to add rule", "error", err)
slog.Error("Auto-save error", "error", err)
slog.Error("Failed to create matcher", "error", err)
os.Exit(1)

Benefits

1. Structured Logging: Key-value pairs make logs easier to parse and query
2. Modern Standard: Uses Go 1.21+'s official structured logging framework
3. Better Observability: Consistent format improves monitoring and debugging
4. No Breaking Changes: All existing functionality preserved

Example Output

The new structured logging provides clearer error messages:

2025/08/28 01:23:53 ERROR Failed to add rule error="weight conflict: rule already exists"

This maintains backward compatibility while providing better structured logging for improved observability and debugging capabilities.

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[Copilot]

Pull Request Overview

This PR migrates from the standard log package to Go's structured logging framework log/slog introduced in Go 1.21, providing consistent structured logging throughout the codebase.

• Replaces log.Printf(), log.Fatalf(), and fmt.Printf() error logging calls with slog.Error()
• Converts fatal logging patterns to use slog.Error() followed by os.Exit(1)
• Adds log/slog and os imports across all affected files

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 20 comments.

Show a summary per file

File	Description
api.go	Updates auto-save error logging in core library
cmd/debug_matching/main.go	Migrates command-line debug tool to structured logging
cmd/target_performance/main.go	Updates performance testing tool error logging
cmd/performance_benchmark/main.go	Converts benchmark tool logging
example/main.go	Updates main example application logging
example/clustered/main.go	Migrates clustered example to structured logging
example/forest_demo/main.go	Updates forest demo logging patterns
example/brokers_demo/main.go	Converts broker demo error handling
example/dimension_consistency/main.go	Updates dimension demo logging
example/multitenant_demo/main.go	Migrates multitenant demo logging
example/weight_conflict_demo/main.go	Updates weight conflict demo error handling

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