refactor(core)!: Add context, config, and structured logging

Introduces `context.Context` to the `FetchCourse` method and its call chain, allowing for cancellable network requests and timeouts. This improves application robustness when fetching remote course data.

A new configuration package centralizes application settings, loading them from environment variables with sensible defaults for base URL, request timeout, and logging.

Standard `log` and `fmt` calls are replaced with a structured logging system built on `slog`, supporting both JSON and human-readable text formats.

This change also includes:
- Extensive benchmarks and example tests.
- Simplified Go doc comments across several packages.

BREAKING CHANGE: The `NewArticulateParser` constructor signature has been updated to accept a logger, base URL, and timeout, which are now supplied via the new configuration system.

internal/interfaces/logger.go

@@ -0,0 +1,27 @@
+// Package interfaces provides the core contracts for the articulate-parser application.
+// It defines interfaces for parsing and exporting Articulate Rise courses.
+package interfaces
+
+import "context"
+
+// Logger defines the interface for structured logging.
+// Implementations should provide leveled, structured logging capabilities.
+type Logger interface {
+	// Debug logs a debug-level message with optional key-value pairs.
+	Debug(msg string, keysAndValues ...any)
+
+	// Info logs an info-level message with optional key-value pairs.
+	Info(msg string, keysAndValues ...any)
+
+	// Warn logs a warning-level message with optional key-value pairs.
+	Warn(msg string, keysAndValues ...any)
+
+	// Error logs an error-level message with optional key-value pairs.
+	Error(msg string, keysAndValues ...any)
+
+	// With returns a new logger with the given key-value pairs added as context.
+	With(keysAndValues ...any) Logger
+
+	// WithContext returns a new logger with context information.
+	WithContext(ctx context.Context) Logger
+}