Suppressing an issue type inserts a double comma when the Suppressed Issues field ends in a delimiter, keeps duplicate IDs, and silently accepts space-separated IDs that never match

How to reproduce:
1. Open a project with com.unity.project-auditor-rules 2.0.0
2. Open Edit > Preferences (macOS: Unity > Settings) > Analysis > Project Auditor
3. Type "PAC1002," into Suppressed Issues (note the trailing comma) and press Enter
4. Window > Analysis > Project Auditor, press "Start Analysis", go to Optimization > Code
5. Select an issue of another type and press "Suppress Issue Type"
6. Go back to Preferences and observe the "Suppressed Issues" fields

Expected results: The field is "PAC1002, PAC2002"
Actual results: The field is "PAC1002,, PAC2002"

Reproducible with: 6000.7.0a4, 6000.7.0b1
Not reproducible with: 6000.6.1f1, 6000.7.0a3 (the field does not exist there)

Reproducible on: macOS Tahoe 26.6.2 (M1)
Not reproducible on: No other environment tested