feat(foundation): create V2 foundation with core interfaces and types

Created complete V2 foundation infrastructure for modular MEV bot:

Core Types (pkg/types/):
- swap.go: SwapEvent with protocol support for 13+ DEXs
- pool.go: PoolInfo with multi-index cache support
- errors.go: Comprehensive error definitions
- Full validation methods and helper functions
- Proper decimal scaling (18 decimals internal representation)

Parser Interface (pkg/parsers/):
- Parser interface for protocol-specific implementations
- Factory interface for routing and registration
- Support for single log and full transaction parsing
- SupportsLog() for dynamic protocol identification

Cache Interface (pkg/cache/):
- PoolCache interface with multi-index support
- O(1) lookups by: address, token pair, protocol, liquidity
- Add, Update, Remove, Count, Clear operations
- Context-aware for cancellation support

Validation Interface (pkg/validation/):
- Validator interface for swap events and pools
- ValidationRules with configurable thresholds
- FilterValid() for batch validation
- Zero address, zero amount, decimal precision checks

Observability (pkg/observability/):
- Logger interface with structured logging (slog)
- Metrics interface with Prometheus integration
- Performance tracking (parse latency, execution)
- Business metrics (arbitrage opportunities, profit)

Project Files:
- go.mod: Module definition with ethereum and prometheus deps
- README.md: Complete project overview and documentation

Architecture Principles:
- Interface-first design for testability
- Single responsibility per interface
- Dependency injection ready
- Observable by default
- 18 decimal internal representation

Ready for Phase 1 implementation:
- All interfaces defined
- Error types established
- Core types validated
- Logging and metrics infrastructure ready

Next: Implement protocol-specific parsers (P2-001 through P2-055)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pkg/observability/logger.go

@@ -0,0 +1,76 @@
+// Package observability provides logging and metrics infrastructure
+package observability
+
+import (
+	"context"
+	"log/slog"
+	"os"
+)
+
+// Logger defines the logging interface
+type Logger interface {
+	// Debug logs a debug message
+	Debug(msg string, args ...any)
+
+	// Info logs an info message
+	Info(msg string, args ...any)
+
+	// Warn logs a warning message
+	Warn(msg string, args ...any)
+
+	// Error logs an error message
+	Error(msg string, args ...any)
+
+	// With returns a logger with additional context fields
+	With(args ...any) Logger
+
+	// WithContext returns a logger with context
+	WithContext(ctx context.Context) Logger
+}
+
+// slogLogger wraps slog.Logger to implement our Logger interface
+type slogLogger struct {
+	logger *slog.Logger
+}
+
+// NewLogger creates a new structured logger
+func NewLogger(level slog.Level) Logger {
+	opts := &slog.HandlerOptions{
+		Level:     level,
+		AddSource: true,
+	}
+
+	handler := slog.NewJSONHandler(os.Stdout, opts)
+	logger := slog.New(handler)
+
+	return &slogLogger{
+		logger: logger,
+	}
+}
+
+func (l *slogLogger) Debug(msg string, args ...any) {
+	l.logger.Debug(msg, args...)
+}
+
+func (l *slogLogger) Info(msg string, args ...any) {
+	l.logger.Info(msg, args...)
+}
+
+func (l *slogLogger) Warn(msg string, args ...any) {
+	l.logger.Warn(msg, args...)
+}
+
+func (l *slogLogger) Error(msg string, args ...any) {
+	l.logger.Error(msg, args...)
+}
+
+func (l *slogLogger) With(args ...any) Logger {
+	return &slogLogger{
+		logger: l.logger.With(args...),
+	}
+}
+
+func (l *slogLogger) WithContext(ctx context.Context) Logger {
+	// Could extract trace ID, request ID, etc. from context
+	return l
+}