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

config_pool_test.go

@@ -14,8 +14,6 @@ func TestNewPoolConfig(t *testing.T) {
 	assert.Equal(t, conf, &PoolConfig{
 		InboxBufferSize:  256,
 		EventsBufferSize: 10,
-		LoggingEnabled:   true,
-		LogLevel:         nil,
 		ConnectionConfig: nil,
 		WorkerConfig:     nil,
 		WorkerFactory:    nil,
@@ -28,8 +26,6 @@ func TestDefaultPoolConfig(t *testing.T) {
 	assert.Equal(t, conf, &PoolConfig{
 		InboxBufferSize:  256,
 		EventsBufferSize: 10,
-		LoggingEnabled:   true,
-		LogLevel:         nil,
 		ConnectionConfig: nil,
 		WorkerConfig:     nil,
 		WorkerFactory:    nil,