Fix race conditions and improve lifecycle safety (#150) (#152)

## Summary
Comprehensive fixes for race conditions, concurrency bugs, and code quality improvements in the lifecycle module and related test files.

## Changes

### Race Condition Fixes
- Fixed data race in `SetChannel()` and `Channel()` by adding mutex protection
- Fixed data race in `StartedAt()` by adding mutex protection
- Fixed test race conditions in `transport` and `interaction` packages where variables were shared between goroutines

### Concurrency Safety Improvements
- Refactored `Close()` to release mutex before calling external code, preventing potential deadlocks
- Made `SetChannel()` reject calls after `Close()` to prevent setting channel on torn-down lifecycle
- Made `SetStatus()` ignore calls after `Close()` to ensure CLOSED is a terminal state
- Added nil check to `SetChannel()` to prevent masking upstream bugs

### Code Quality Improvements
- Refactored `Close()` to extract helper methods: `closeChannel()`, `closeConnection()`, `cleanupRegistry()`, `cleanupForwarder()`
- Fixed `isClosedError()` to remove redundant string comparison
- Added `PortRegistry` interface for better interface segregation (removed dependency on full `port.Port`)
- Made `cleanupRegistry()` conditional on non-empty slug to avoid unnecessary registry calls
- Fixed `startedAt` to be set when session starts running instead of at object creation

Reviewed-on: #150
Co-authored-by: Bagas <bagas@fossy.my.id>
Co-committed-by: Bagas <bagas@fossy.my.id>

Reviewed-on: #152

internal/transport/http_test.go

@@ -55,8 +55,7 @@ func TestHTTPServer_Serve(t *testing.T) {
 
 	go func() {
 		time.Sleep(100 * time.Millisecond)
-		err = listener.Close()
-		assert.NoError(t, err)
+		_ = listener.Close()
 	}()
 
 	err = srv.Serve(listener)

internal/transport/https_test.go

@@ -63,8 +63,7 @@ func TestHTTPSServer_Serve(t *testing.T) {
 
 	go func() {
 		time.Sleep(100 * time.Millisecond)
-		err = listener.Close()
-		assert.NoError(t, err)
+		_ = listener.Close()
 	}()
 
 	err = srv.Serve(listener)

internal/transport/tcp_test.go

@@ -45,8 +45,7 @@ func TestTCPServer_Serve(t *testing.T) {
 
 	go func() {
 		time.Sleep(100 * time.Millisecond)
-		err = listener.Close()
-		assert.NoError(t, err)
+		_ = listener.Close()
 	}()
 
 	err = srv.Serve(listener)