fix: resolve SideEffectNotAllowedException in intention previews (#11894)

* fix: use Dispatchers.Default to avoid SideEffectNotAllowedException in JetBrains intention previews

DocumentChangeTracker and ActiveHandlerManager used Dispatchers.Main which
schedules work via INVOKE_LATER. JetBrains forbids this during intention
preview computation (autocomplete, inspections), throwing
SideEffectNotAllowedException. Neither class requires EDT for its coroutine
work, so switching to Dispatchers.Default resolves the issue.

Fixes #9463, #8035

* fix: use limitedParallelism(1) to prevent race conditions

Dispatchers.Default allows concurrent execution on a thread pool,
which breaks thread-safety for shared mutable state that was previously
serialized on the Main/EDT dispatcher. Using limitedParallelism(1)
preserves single-threaded execution while still avoiding the
SideEffectNotAllowedException from Dispatchers.Main.

Author: RomneyDa

extensions/intellij/src/main/kotlin/com/github/continuedev/continueintellijextension/listeners/ActiveHandlerManager.kt

@@ -56,7 +56,7 @@ interface CursorMovementHandler {
 @Service(Service.Level.PROJECT)
 class ActiveHandlerManager(private val project: Project) : SelectionListener, CaretListener, DumbAware {
 
-    private val coroutineScope = CoroutineScope(Dispatchers.Main + SupervisorJob())
+    private val coroutineScope = CoroutineScope(Dispatchers.Default.limitedParallelism(1) + SupervisorJob())
     private var activeHandler: CursorMovementHandler? = null
     private var isHandlingEvent = false
 

extensions/intellij/src/main/kotlin/com/github/continuedev/continueintellijextension/listeners/DocumentChangeTracker.kt

@@ -13,7 +13,7 @@ import kotlinx.coroutines.*
 @Service(Service.Level.PROJECT)
 class DocumentChangeTracker(private val project: Project) : DocumentListener {
 
-    private val coroutineScope = CoroutineScope(Dispatchers.Main + SupervisorJob())
+    private val coroutineScope = CoroutineScope(Dispatchers.Default.limitedParallelism(1) + SupervisorJob())
     private var typingHandler: TypingSessionHandler? = null
     private var typingSessionTimer: Job? = null