Description

Resolves #651 by introducing a debounce timer for filter text input in DataGridFilterBar:

1. Debounce Mechanism:

   • Added a 150ms debounce Timer to _DataGridFilterBarState.
   • Rapid keystrokes no longer trigger sequential full dataset filtering on each character.
   • Autocomplete suggestions continue to update instantly for zero typing lag.

2. Immediate Executions & Cleanup:

   • Enter key submission (onSubmitted) cancels pending debounce and immediately triggers filtering.
   • Clear button tap cancels pending debounce and immediately clears the filter.
   • Timer is cleanly cancelled on widget dispose().

3. Testing:

   • Added unit and widget tests in test/features/workspace/data_grid_filter_bar_test.dart verifying debounced emission, immediate Enter submission, and clear button cancellation.
   • All 183 tests pass with 0 analyze issues.

Closes #651