refactor(editor): decouple QueryaCodeEditor from highlight controller lifecycle and manage at session level #1366

Summary

In lib/core/editor/querya_code_editor.dart (lines 62–185):
QueryaCodeEditor is currently burdened with multiple non-UI responsibilities:

1. It maintains two distinct controllers simultaneously: an internal _highlightController and an external widget.controller (_plainController).
2. It sets up two-way listeners (_syncFromExternal / _syncToExternal) that perform full-string equality comparisons on every single keystroke (perf(editor): eliminate two-way controller bouncing and full-string comparisons in QueryaCodeEditor #1352).
3. It performs hash calculations on tokenColors and recreates controllers inside build() during theme transitions (perf(theme): cache tokenColorsHash on QueryaTheme to eliminate Object.hashAll in QueryaCodeEditor.build() #1353, perf(theme): eliminate continuous QueryaHighlightController recreation during AnimatedQueryaTheme transitions #1358).

This violates clean widget architecture by making the presentation editor responsible for highlight controller lifecycle and state synchronization.

Proposed Solution

1. Transform QueryaCodeEditor into a clean presentation widget that accepts a single, already-configured TextEditingController (which can be a QueryaHighlightController or plain TextEditingController).
2. Move highlight controller instantiation, grammar loading, and lifecycle management to SqlQueryTabSession (or a dedicated CodeEditorControllerFactory).
3. Eliminate the two-way sync loop and full-string comparisons between controllers.

Acceptance Criteria

• QueryaCodeEditor does not maintain dual synchronized controllers.
• Text editing and syntax highlighting remain fully functional across all workspaces.
• Keystroke overhead during typing is reduced.