Migrate logging to go-mana-component; delete logging/ package

Replaces the flat key-value logging scheme with component-based structured
logging via go-mana-component. Each layer (pool, worker, connection) builds
its own component identity and derives a *slog.Logger from a caller-supplied
slog.Handler.

- Delete logging/ package (logging.go, logging_test.go)
- Strip LoggingEnabled and LogLevel from ConnectionConfig, PoolConfig,
 WorkerConfig; remove associated option funcs
- Change NewConnection and NewConnectionFromSocket to accept ctx and
 slog.Handler instead of *slog.Logger; constructors build component
 identity via MustNew/MustExtend internally
- Change WorkerFactory, NewWorker, connect, and RunDialer to carry
 slog.Handler; remove PoolPlugin.Handler
- Change NewPool to establish pool component identity via MustNew;
 remove pool_id field, PoolPlugin.ID, and ErrInvalidPoolID
- Fix data race in MockSlogHandler: WithAttrs now shares parent mutex
 pointer rather than allocating a new one per child
- Run go fix

errors.go

@@ -10,10 +10,9 @@ var (
 	InvalidBufferSize       = errors.New("buffer size must be greater than zero")
 
 	// Pool errors
-	ErrInvalidPoolID = errors.New("pool id cannot be empty")
-	ErrPoolClosed    = errors.New("pool is closed")
-	ErrPeerNotFound  = errors.New("peer not found")
-	ErrPeerExists    = errors.New("peer already exists")
+	ErrPoolClosed   = errors.New("pool is closed")
+	ErrPeerNotFound = errors.New("peer not found")
+	ErrPeerExists   = errors.New("peer already exists")
 
 	// Worker errors
 	ErrConnectionUnavailable = errors.New("connection unavailable")