Fix race conditions and improve lifecycle safety (#150)

## 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>

internal/session/interaction/interaction_test.go

@@ -1922,10 +1922,6 @@ func TestInteraction_Start_ProtocolSelection(t *testing.T) {
 			time.Sleep(50 * time.Millisecond)
 
 			i := mockInteraction.(*interaction)
-			if i.program != nil {
-				assert.NotNil(t, i.program, "program should be initialized")
-			}
-
 			i.Stop()
 
 			mockConfig.AssertExpectations(t)